Component

ConstraintType

Overview

ConstraintType is a header library to constraint type in template parameters. It is useful and convenient for generic programming and provide backward compatibility from C++ 14 to C++ 20. When you use C++ 20 or greater standards it will use concept instead of constant expression.

Introduction

Constraint non-generic type with a type list

ConstructBasicEligibleType(BasicEligibleType, int, A, std::thread);   // ->int||A||std::thread

Constraint multi-dimension generic type

AddTypeLayer(0, std::list);
AddTypeLayer(0, std::deque);
AddTypeLayer(1, std::vector);
ConstructEligibleType(EligibleType, 2, 1, int);   // ->std::vector<std::list<int>||std::deque<int>>

Constraint template parameter with index

template<typename T1, typename T2>
struct A {};
AddTypeLayerWithPosition(0, 1, A);
ConstructEligibleTypeWithPosition(EligibleType, 1, 0, 1, double);   // ->A<?,double>

Use Any to skip matching on specified layer or underlying type

AddTypeLayer(0, Any);
ConstructEligibleType(EligibleType, 1, 0, char, short, int, long long);   // ->?<char||short||int||long long>

Constraint or get constant expression

template<typename T1, typename T2, int V>
struct A {};
AddValueLayerWithPosition(0, 2, A, T, T, V);
ConstructEligibleValueWithPosition(EligibleValue, 1, 0, 2, std::tuple<std::greater<void>, std::less<void>>, 5, 10);         // ->A<?,?,(5,10)>

Error message

You can use

#define ShowErrorMessage

to show the following types of error message:
ErrorType<Type,Layer,Index> will tell you compile failed on what Type which Layer and which Index. ErrorValue<ValueToBeChecked,Operator,ValueUserProvided> will tell you compile failed on what ValueToBeChecked what Operator and what ValueUserProvided.
This option is closed by default, so you can use this library on SFINAE.

Installation

If you are using cmake, then just add

# Show actual C++ version for MSVC
# Use compliant C11 preprocessor for MSVC
if(MSVC)
    target_compile_options(TARGET_NAME PRIVATE /Zc:__cplusplus /Zc:preprocessor)
    target_compile_definitions(TARGET_NAME PRIVATE ML99_ALLOW_POOR_DIAGNOSTICS)
# Metalang99 relies on heavy macro machinery. To avoid useless macro expansion
# errors, please write this:
elseif(CMAKE_C_COMPILER_ID STREQUAL "Clang")
    target_compile_options(TARGET_NAME PRIVATE -fmacro-backtrace-limit=1)
elseif(CMAKE_C_COMPILER_ID STREQUAL "GNU")
    target_compile_options(TARGET_NAME PRIVATE -ftrack-macro-expansion=0)
endif()

include(FetchContent)
FetchContent_Declare(
    ConstraintType
    URL https://github.com/yonghenghuanmie/Component/archive/refs/tags/v1.4.0.tar.gz # v1.4.0
    SOURCE_SUBDIR ConstraintType
)
FetchContent_MakeAvailable(ConstraintType)
target_link_libraries(TARGET_NAME PRIVATE ConstraintType)

to your CMakeLists.txt and replace TARGET_NAME with correct target name.
Or you can just download ConstraintType.h and download requirement metalang99.

Usage

For more example you can see ConstraintType/ConstraintType.cpp for concept or ConstraintType/ConstraintTypeBackwardCompatibility.cpp for legacy.