Check for presence of function

[Philippe Sigaud]

On Sun, Mar 23, 2014 at 1:40 PM, Steve Teale
<steve.teale at britseyeview.com> wrote:
> What's the cool/idiomatic D way to test at compile time if a struct has a
> member function with a particular signature? Along the lines of:
>
> struct Unrelated
> {
>    ...
> }
>
> template isSomething(T)
> {
>     enum bool isSomething = is(typeof(
>     (inout int = 0)
>     {
>        T???; // has a function void doSomething(Unrelated* up);
>        // etc
>     }));
> }
>
> struct Thingie
> {
>    ...
> }
>
> static assert(isSomething!(Thingie));

You can use __traits(compiles, /* some code */), like this:


struct Unrelated {}

template isSomething(T)
{
    enum bool isSomething = __traits(compiles,
        {
           Unrelated* up;
           T.init.doSomething(up);
        }
    );
}

struct Thingie
{
    void doSomething(Unrelated* up) {}
}

void main()
{
    pragma(msg, isSomething!Thingie); // true
    pragma(msg, isSomething!Unrelated); // false
    pragma(msg, isSomething!int); // false
}