mirror of https://github.com/ARMmbed/mbed-os.git
Span: amend documentation
Vincent Coubard
parent
95fc284a83
commit
4e7fa91b94
203
platform/Span.h
203
platform/Span.h
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@ -33,19 +33,130 @@ namespace mbed {
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#define SPAN_DYNAMIC_EXTENT -1
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/**
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* View to an array.
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* Non owning view to a sequence of contiguous elements.
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*
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* Spans encapsulate the pointer to an array and its size into a single object.
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* However, it does not manage the lifetime of the array viewed. You can use
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* instances of Span to replace the traditional pair of pointer and size
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* arguments in function calls.
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* Spans encapsulate a pointer to a sequence of contiguous elements and its size
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* into a single object. Span can replace the traditional pair of pointer and
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* size arguments passed as array definition in function calls.
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*
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* You can use the size member function to query the number of elements present
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* in the array, and the subscript operator allow code using this object to
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* access the content of the array viewed.
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* @paragraph Operations
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*
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* Subspans can be created with the help of the functions first(), last() and
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* subspan().
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* Span objects can be copied and assigned like regular value types with the help
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* of copy constructor and copy assignment (=) operator.
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*
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* Elements of the object can be retrieved with the subscript ([]) operator. The
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* pointer to the first element of the sequence viewed can be accessed with data()
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* while the function size() returns the number of elements in the sequence and
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* empty() informs if the there is any element in the sequence.
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*
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* Span can be sliced from the beginning of the sequence (first()), from the end
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* of the sequence (last()) or from an arbitrary point of the sequence (subspan()).
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*
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* @paragraph Size encoding
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*
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* The size of the sequence can be encoded in the type itself or in the value of
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* the instance with the help of the template parameter Extent:
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*
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* - Span<uint8_t, 6>: Span over a sequence of 6 element
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* - Span<uint8_t>: Span over an arbitrary long sequence.
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*
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* When the size is encoded in the type itself, it is guaranteed that the Span
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* view a valid sequence (not empty() and not NULL). The type system also prevent
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* automatic conversion from Span of different sizes. Finally, the size of the
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* span object is a single pointer.
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*
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* When the size of the sequence viewed is encoded in the Span value, span
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* instances can view invalid sequence (empty and NULL pointer). The function
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* empty() helps client code to decide if valid content is being viewed or not.
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*
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* @paragraph Example
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*
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* - Encoding fixed size array: Array values in parameter decays automatically
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* to pointer which leaves room for subtitle bugs:
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*
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* @code
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* typedef uint8_t mac_address_t[6];
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* void process_mac(mac_address_t);
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*
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* // compile just fine
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* uint8_t* invalid_value = NULL;
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* process_mac(invalid_value);
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*
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*
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* // correct way
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* typedef Span<uint8_t, 6> mac_address_t;
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* void process_mac(mac_address_t);
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*
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* // compilation error
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* uint8_t* invalid_value = NULL;
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* process_mac(invalid_value);
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*
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* // compilation ok
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* uint8_t valid_value[6];
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* process_mac(valid_value);
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* @endcode
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*
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* - Arbitrary buffer: When dealing with multiple buffers, it becomes painful to
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* keep track of every buffer size and pointer.
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*
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* @code
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* const uint8_t options_tag[OPTIONS_TAG_SIZE];
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*
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* struct parsed_value_t {
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* uint8_t* header;
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* uint8_t* options;
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* uint8_t* payload;
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* size_t payload_size;
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* }
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*
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* parsed_value_t parse(uint8_t* buffer, size_t buffer_size) {
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* parsed_value_t parsed_value { 0 };
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*
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* if (buffer != NULL && buffer_size <= MINIMAL_BUFFER_SIZE) {
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* return parsed_value;
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* }
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*
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* parsed_value.header = buffer;
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* parsed_value.header_size = BUFFER_HEADER_SIZE;
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*
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* if (memcmp(buffer + HEADER_OPTIONS_INDEX, options_tag, sizeof(options_tag)) == 0) {
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* options = buffer + BUFFER_HEADER_SIZE;
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* payload = buffer + BUFFER_HEADER_SIZE + OPTIONS_SIZE;
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* payload_size = buffer_size - BUFFER_HEADER_SIZE + OPTIONS_SIZE;
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* } else {
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* payload = buffer + BUFFER_HEADER_SIZE;
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* payload_size = buffer_size - BUFFER_HEADER_SIZE;
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* }
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*
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* return parsed_value;
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* }
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*
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*
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* //with span
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* struct parsed_value_t {
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* Span<uint8_t> header;
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* Span<uint8_t> options;
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* Span<uint8_t> payload;
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* }
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*
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* parsed_value_t parse(Span<uint8_t> buffer) {
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* parsed_value_t parsed_value;
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*
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* if (buffer.size() <= MINIMAL_BUFFER_SIZE) {
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* return parsed_value;
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* }
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*
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* parsed_value.header = buffer.first(BUFFER_HEADER_SIZE);
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*
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* if (buffer.subspan<HEADER_OPTIONS_INDEX, sizeof(options_tag)>() == option_tag) {
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* options = buffer.supspan(parsed_value.header.size(), OPTIONS_SIZE);
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* }
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*
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* payload = buffer.subspan(parsed_value.header.size() + parsed_value.options.size());
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*
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* return parsed_value;
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* }
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* @endcode
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*
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* @note You can create Span instances with the help of the function template
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* make_Span() and make_const_Span().
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@ -53,9 +164,9 @@ namespace mbed {
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* @note Span<T, Extent> objects can be implicitly converted to Span<T> objects
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* where required.
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*
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* @tparam ElementType type of objects held in the array viewed.
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* @tparam ElementType type of objects viewed by the Span.
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*
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* @tparam Extent The size of the array viewed. The default value
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* @tparam Extent The size of the contiguous sequence viewed. The default value
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* SPAN_DYNAMIC_SIZE is special as it allows construction of Span objects of
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* any size (set at runtime).
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*/
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@ -90,7 +201,7 @@ struct Span {
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MBED_STATIC_ASSERT(Extent >= 0, "Invalid extent for a Span");
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/**
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* Construct an empty span.
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* Construct an empty Span.
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*
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* @post a call to size() will return 0, and data() will return NULL.
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*
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@ -112,7 +223,7 @@ struct Span {
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* @param count Number of elements viewed.
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*
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* @pre [ptr, ptr + count) must be be a valid range.
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* @pre count must be equal to extent.
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* @pre count must be equal to Extent.
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*
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* @post a call to size() will return Extent and data() will return @p ptr.
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*/
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@ -153,9 +264,9 @@ struct Span {
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_data(elements) { }
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/**
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* Return the size of the array viewed.
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* Return the size of the sequence viewed.
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*
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* @return The number of elements present in the array viewed.
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* @return The size of the sequence viewed.
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*/
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index_type size() const
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{
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@ -163,9 +274,9 @@ struct Span {
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}
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/**
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* Return if the array is empty or not.
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* Return if the sequence is empty or not.
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*
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* @return true if the array is empty and false otherwise
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* @return true if the sequence is empty and false otherwise
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*/
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bool empty() const
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{
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@ -190,10 +301,10 @@ struct Span {
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}
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/**
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* Return a pointer to the first element of the sequence or NULL if the span
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* Return a pointer to the first element of the sequence or NULL if the Span
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* is empty().
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*
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* @return The pointer to the first element of the span.
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* @return The pointer to the first element of the Span.
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*/
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pointer data() const
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{
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@ -246,7 +357,7 @@ struct Span {
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* is equal to SPAN_DYNAMIC_EXTENT then a span starting at offset and
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* containing the rest of the elements is returned.
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*
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* @return
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* @return A subspan of this starting at Offset and Count long.
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*/
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template<std::ptrdiff_t Offset, std::ptrdiff_t Count>
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Span<element_type, Count == SPAN_DYNAMIC_EXTENT ? Extent - Offset : Count>
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@ -324,7 +435,7 @@ private:
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};
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/**
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* Span specialisation that handle dynamic array size.
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* Span specialisation that handle dynamic size.
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*/
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template<typename ElementType>
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struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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@ -355,7 +466,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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static const index_type extent = SPAN_DYNAMIC_EXTENT;
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/**
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* Construct an empty span.
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* Construct an empty Span.
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*
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* @post a call to size() will return 0, and data() will return NULL.
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*
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@ -437,9 +548,9 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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}
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/**
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* Return if the array is empty or not.
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* Return if the sequence viewed is empty or not.
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*
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* @return true if the array is empty and false otherwise
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* @return true if the sequence is empty and false otherwise
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*/
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bool empty() const
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{
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@ -447,7 +558,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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}
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/**
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* Access to an element of the array.
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* Access to an element of the sequence.
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*
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* @param index Element index to access.
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*
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@ -464,9 +575,9 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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}
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/**
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* Get the raw pointer to the array.
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* Get the raw pointer to the sequence viewed.
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*
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* @return The raw pointer to the array.
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* @return The raw pointer to the first element viewed.
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*/
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pointer data() const
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{
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@ -474,7 +585,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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}
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/**
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* Create a new span over the first @p Count elements of the existing view.
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* Create a new Span over the first @p Count elements of the existing view.
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*
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* @tparam Count The number of element viewed by the new Span
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*
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@ -489,7 +600,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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}
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/**
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* Create a new span over the last @p Count elements of the existing view.
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* Create a new Span over the last @p Count elements of the existing view.
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*
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* @tparam Count The number of element viewed by the new Span
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*
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@ -513,7 +624,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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* is equal to SPAN_DYNAMIC_EXTENT then a span starting at offset and
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* containing the rest of the elements is returned.
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*
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* @return
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* @return A subspan of this starting at Offset and Count long.
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*/
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template<std::ptrdiff_t Offset, std::ptrdiff_t Count>
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Span<element_type, Count == SPAN_DYNAMIC_EXTENT ? SPAN_DYNAMIC_EXTENT : Count>
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@ -542,7 +653,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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}
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/**
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* Create a new span over the last @p count elements of the existing view.
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* Create a new Span over the last @p count elements of the existing view.
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*
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* @param count The number of element viewed by the new Span
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*
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@ -566,7 +677,7 @@ struct Span<ElementType, SPAN_DYNAMIC_EXTENT> {
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* is equal to SPAN_DYNAMIC_EXTENT then a span starting at offset and
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* containing the rest of the elements is returned.
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*
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* @return
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* @return A subspan of this starting at offset and count long.
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*/
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Span<element_type, SPAN_DYNAMIC_EXTENT> subspan(
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index_type offset, index_type count = SPAN_DYNAMIC_EXTENT
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@ -593,8 +704,8 @@ private:
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* @param lhs Left hand side of the binary operation.
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* @param rhs Right hand side of the binary operation.
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*
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* @return True if arrays in input have the same size and the same content
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* and false otherwise.
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* @return True if Spans in input have the same size and the same content and
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* false otherwise.
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*/
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template<typename T, typename U, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
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bool operator==(const Span<T, LhsExtent> &lhs, const Span<U, RhsExtent> &rhs)
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@ -616,8 +727,8 @@ bool operator==(const Span<T, LhsExtent> &lhs, const Span<U, RhsExtent> &rhs)
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* @param lhs Left hand side of the binary operation.
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* @param rhs Right hand side of the binary operation.
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*
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* @return True if arrays in input have the same size and the same content
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* and false otherwise.
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* @return True if elements in input have the same size and the same content and
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* false otherwise.
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*/
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template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
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bool operator==(const Span<T, LhsExtent> &lhs, T (&rhs)[RhsExtent])
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@ -626,12 +737,12 @@ bool operator==(const Span<T, LhsExtent> &lhs, T (&rhs)[RhsExtent])
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}
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/**
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* Equality operation between a span and a reference to a C++ array.
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* Equality operation between a Span and a reference to a C++ array.
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*
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* @param lhs Left hand side of the binary operation.
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* @param rhs Right hand side of the binary operation.
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*
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* @return True if arrays in input have the same size and the same content
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* @return True if elements in input have the same size and the same content
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* and false otherwise.
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*/
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template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
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@ -646,8 +757,8 @@ bool operator==(T (&lhs)[LhsExtent], const Span<T, RhsExtent> &rhs)
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* @param lhs Left hand side of the binary operation.
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* @param rhs Right hand side of the binary operation.
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*
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* @return True if arrays in input do not have the same size or the same
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* content and false otherwise.
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* @return True if arrays in input do not have the same size or the same content
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* and false otherwise.
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*/
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template<typename T, typename U, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
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bool operator!=(const Span<T, LhsExtent> &lhs, const Span<U, RhsExtent> &rhs)
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@ -656,12 +767,12 @@ bool operator!=(const Span<T, LhsExtent> &lhs, const Span<U, RhsExtent> &rhs)
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}
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/**
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* Not Equal operation between a span and a reference to a C++ array.
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* Not Equal operation between a Span and a reference to a C++ array.
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*
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* @param lhs Left hand side of the binary operation.
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* @param rhs Right hand side of the binary operation.
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*
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* @return True if arrays in input have the same size and the same content
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* @return True if elements in input have the same size and the same content
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* and false otherwise.
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*/
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template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
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@ -671,12 +782,12 @@ bool operator!=(const Span<T, LhsExtent> &lhs, T (&rhs)[RhsExtent])
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}
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/**
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* Not Equal operation between a span and a reference to a C++ array.
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* Not Equal operation between a Span and a reference to a C++ array.
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*
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* @param lhs Left hand side of the binary operation.
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* @param rhs Right hand side of the binary operation.
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*
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* @return True if arrays in input have the same size and the same content
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* @return True if elements in input have the same size and the same content
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* and false otherwise.
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*/
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template<typename T, ptrdiff_t LhsExtent, ptrdiff_t RhsExtent>
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@ -728,7 +839,7 @@ Span<T, Extent> make_Span(T *elements)
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*
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* @tparam T Type of elements held in array_ptr.
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*
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* @param array_ptr The pointer to the array to viewed.
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* @param array_ptr The pointer to the array viewed.
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* @param array_size The number of T elements in the array.
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*
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* @return The Span to array_ptr with a size of array_size.
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