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https://github.com/aantron/better-enums.git
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82 lines
2.6 KiB
C++
82 lines
2.6 KiB
C++
// Compile-time iteration. This example generates an approximation of enum
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// declarations (without explicit "="" settings) at run time. The storage space
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// for this is reserved at compile time, however.
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#include <cassert>
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#include <cstring>
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#include <iostream>
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#include <enum.h>
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CONSTEXPR_TO_STRING_ENUM(Channel, int, Red, Green, Blue)
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CONSTEXPR_TO_STRING_ENUM(Depth, int, TrueColor, HighColor)
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// Computes the length of a string.
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constexpr size_t string_length(const char *s, size_t index = 0)
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{
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return s[index] == '\0' ? index : string_length(s, index + 1);
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}
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// Runs over all the constants in an enum and adds up the lengths of their
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// names.
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template <typename Enum>
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constexpr size_t total_names_length(size_t accumulator = 0, size_t index = 0)
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{
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return
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index == Enum::_size ? accumulator :
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total_names_length<Enum>
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(accumulator + string_length(Enum::_names()[index]), index + 1);
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}
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// Computes the total length of an ENUM declaration, assuming the type is int.
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// The summands correspond to each of the tokens and spaces (i.e., "ENUM", "(",
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// etc.). (Enum::_size - 1) * 2 is added to account for each comma and space
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// following each constant name, except for the last one. The final 1 is added
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// to account for the null terminator.
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template <typename Enum>
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constexpr size_t declaration_length()
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{
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return
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4 + 1 + string_length(Enum::_name()) + 1 + 1 + 3 + 1 + 1 +
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total_names_length<Enum>() + (Enum::_size - 1) * 2 + 1 + 1 + 1;
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}
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// Formats the declaration into space already reserved.
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template <typename Enum>
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void format_declaration(char *storage)
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{
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std::strcat(storage, "ENUM(");
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std::strcat(storage, Enum::_name());
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std::strcat(storage, ", int, ");
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for (auto name_iterator = Enum::_names().begin();
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name_iterator < Enum::_names().end() - 1; ++name_iterator) {
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std::strcat(storage, *name_iterator);
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std::strcat(storage, ", ");
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}
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std::strcat(storage, Enum::_names()[Enum::_size - 1]);
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std::strcat(storage, ");");
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assert(std::strlen(storage) == declaration_length<Enum>() - 1);
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}
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// Reserve space for the formatted declaration of each enum. These buffers
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// should be zeroed at load time or during code generation, so, semantically,
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// they contain the empty string.
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char channel_declaration[declaration_length<Channel>()];
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char depth_declaration[declaration_length<Depth>()];
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int main()
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{
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format_declaration<Channel>(channel_declaration);
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std::cout << channel_declaration << std::endl;
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format_declaration<Depth>(depth_declaration);
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std::cout << depth_declaration << std::endl;
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return 0;
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}
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