Tao He sighingnow

Why COW was deemed ungood for std::string.

COW, short for copy on write, is a way to implement mutable strings so that creating strings and logically copying strings, is reduced to almost nothing; conceptually they become free operations like no-ops.

Basic idea: to share a data buffer among string instances, and only make a copy for a specific instance (the copy on write) when that instance's data is modified. The general cost of this is only an extra indirection for accessing the value of a string, so a COW implementation is highly desirable. And so the original C++ standard, C++98, and its correction C++03, had special support for COW implementations, and e.g. the g++ compiler's std::string implementations used COW.

So why was that support dropped in C++11?

In particular, would the same reason or reasons apply to a reference counted immutable string value class?

	class GPTModel:
	def __init__(
	self,
	name: str = None,
	vocab_size: int = 51200,
	sequence_length: int = 2048,
	attention_heads: int = 32,
	hidden_size: int = 2304,
	layers: int = 24,
	micro_batch_size: int = 1,


	template <typename U>
	struct A_trait {
	using T = int;
	};

	template <typename U, template <typename ...> class Trait = A_trait>
	struct A {
	using T = typename Trait<U>::T;
	};

	function(print_cmake_variables)
	get_cmake_property(_variableNames VARIABLES)
	list (SORT _variableNames)
	foreach (_variableName ${_variableNames})
	if (ARGV0)
	unset(MATCHED)
	string(REGEX MATCH ${ARGV0} MATCHED ${_variableName})
	if (NOT MATCHED)
	continue()
	endif()

	# Get all propreties that cmake supports
	if(NOT CMAKE_PROPERTY_LIST)
	execute_process(COMMAND cmake --help-property-list OUTPUT_VARIABLE CMAKE_PROPERTY_LIST)

	# Convert command output into a CMake list
	string(REGEX REPLACE ";" "\\\\;" CMAKE_PROPERTY_LIST "${CMAKE_PROPERTY_LIST}")
	string(REGEX REPLACE "\n" ";" CMAKE_PROPERTY_LIST "${CMAKE_PROPERTY_LIST}")
	endif()

	list(APPEND CMAKE_PROPERTY_LIST "IMPORTED_LOCATION")

	macro(find_openssl_libraries)
	if (APPLE)
	# If we're on OS X check for Homebrew's copy of OpenSSL instead of Apple's
	if (NOT OpenSSL_DIR)
	find_program(HOMEBREW brew)
	if (HOMEBREW STREQUAL "HOMEBREW-NOTFOUND")
	message(WARNING "Homebrew not found: not using Homebrew's OpenSSL")
	if (NOT OPENSSL_ROOT_DIR)
	message(WARNING "Use -DOPENSSL_ROOT_DIR for non-Apple OpenSSL")
	endif()