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digitalmars.D.announce - Re: Default value currying template

On 8/2/12, Andrej Mitrovic <andrej.mitrovich gmail.com> wrote:
 On 8/2/12, Walter Bright <newshound2 digitalmars.com> wrote:
 Known issue, it's an inevitable result (it never worked right anyway):


 P.S. You might want to monitor the beta releases.

I've posted about that exact Derelict case in Issue 3866 during the betas, but nobody replied. But a library solution could be made if one wants to use an inner alias. Maybe we even have one in Phobos? Something like: void foo(void delegate(string s, bool isTrue) dg) { alias DefVal!(dg, true) deg; // use deg as if it were dg() with default for 'isTrue' } Not the most readable code.. but it's similar to curry (except backwards) I guess.

So here's an implementation: import std.stdio; import std.traits; import std.typetuple; template DefVal(alias Call, DefVals...) if (isCallable!Call && DefVals.length <= ParameterTypeTuple!Call.length) { auto DefVal(T...)(T args) { return Call(args, Reverse!DefVals); } } void foo(int x, float y, string z) { writefln("x: %s, y: %s, z: %s", x, y, z); } void main() { alias DefVal!(foo, "a", 1.0, 1) fooDef3; alias DefVal!(foo, "a", 1.0) fooDef2; alias DefVal!(foo, "a") fooDef1; alias DefVal!(foo) fooDef0; fooDef0(1, 1.0, "a"); fooDef1(1, 1.0); fooDef2(1); fooDef3(); } Essentially it's like the reverse of curry().
Aug 02 2012