Re: New to D and mimicking C++ : how to implement std::integral_constant<>?

[Basile B. via Digitalmars-d-learn]

On Monday, 7 November 2016 at 23:03:32 UTC, Picaud Vincent wrote:
 I need:
1/ a way to detect compile-time constant vs "dynamic" values

/**
 * Indicates if something is a value known at compile time.
 *
 * Params:
 *      V = The value to test.
 *      T = Optional, the expected value type.
 */
template isCompileTimeValue(alias V, T...)
if (T.length == 0 || (T.length == 1 && is(T[0])))
{
    enum isKnown = is(typeof((){enum v = V;}));
    static if (!T.length)
        enum isCompileTimeValue = isKnown;
    else
        enum isCompileTimeValue = isKnown && is(typeof(V) == 
T[0]);
}
///
unittest
{
    string a;
    enum b = "0";
    enum c = 0;
    static assert(!isCompileTimeValue!a);
    static assert(isCompileTimeValue!b);
    static assert(isCompileTimeValue!c);
    static assert(isCompileTimeValue!(b,string));
    static assert(isCompileTimeValue!(c,int));
    static assert(!isCompileTimeValue!(c,char));
    static assert(!isCompileTimeValue!(char));
}