如果指定的值在类型的范围内，则在编译时检查 [英] Checking at compile time if specified value is in a range of a type

问题描述

可以检查：

template<class IntType,IntType value>
struct X{};

我的意思是，可以检查用户提供的值将fit到IntType（可以是任何std整数类型）类型？例如，我想检测这样的东西：

What I mean by this is, is it possible to check that value supplied by user will "fit" into IntType (which can be any of std integer types) type? For example, I would like to detect something like this:

X<char,300> a;//here 300 is out of range and I would like to be able to detect that.

推荐答案

> X 的原始未编辑问题的签名，它很容易实现使用 Boost 。整数：

#include <boost/static_assert.hpp>
#include <boost/cstdint.hpp>
#include <boost/integer_traits.hpp>

template<
    typename IntType,
    boost::uint64_t Value,
    bool IsSigned = boost::integer_traits<IntType>::is_signed
>
struct validate_range;

template<typename IntType, boost::uint64_t Value>
struct validate_range<IntType, Value, true>
{
    typedef boost::integer_traits<IntType> traits_t;
    static bool const value =
        static_cast<boost::int64_t>(Value) >= traits_t::const_min &&
        static_cast<boost::int64_t>(Value) <= traits_t::const_max;
};

template<typename IntType, boost::uint64_t Value>
struct validate_range<IntType, Value, false>
{
    typedef boost::integer_traits<IntType> traits_t;
    static bool const value =
        Value >= traits_t::const_min &&
        Value <= traits_t::const_max;
};

template<typename IntType, boost::uint64_t Value>
struct X
{
    BOOST_STATIC_ASSERT_MSG(
        (validate_range<IntType, Value>::value),
        "Value constant is out of range"
    );
};

int main()
{
    X<char, -2> x1;             // fails iif char is unsigned by default
    X<char, 2> x2;              // fine
    X<char, 255> x3;            // fails iif char is signed by default
    X<unsigned char, -2> x4;    // fails
    X<unsigned char, 255> x5;   // fine
    X<unsigned char, 300> x6;   // fails
}

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