On 2013-03-22 11:17, J wrote:
With credit for inspiration to David Medlock in this post-- http://forum.dlang.org/thread/d9lnrr$26q3$1...@digitaldaemon.com ...// Tongue firmly in cheek, I'd like to introduce // the NAPAPISS principle: (with apologies to SFINAE and RAII) // NAPAPISS = NAmed Parameters Are simply Passed in a Struct, Silly. // Yes, indeed, maybe this is what happens after drinking too much of // the fine wine products from the Napa valley... you start having // wild flights of fancy of how D might surprisingly soon have // named parameters.... import std.stdio; import std.c.stdlib; void main(string[] arg) { // this works today: but with the drawback that the // named params must be known at compile time... // Here is a named param call, // as compact as I could get it (see struct below for actual definition). auto a = myfunc!q{ z= 2; x = -123; y = 200 }(0)(); // calls opCall writeln("a=", a); // prints "a=yo", as returned from opCall // And here's the runtime version, unfortunately you have to // pre-declare g because otherwise it won't survive the scope, and // the return value from myfunc.opCall would become inaccessible. string g; with(myfunc!()(0)) { x=rand() % 40; y=x/2; z=y/2; g = call(); // as a side effect, prints 'X 7, Y 3, Z 1' } writeln("g=", g); // prints "g=yo", as returned from opCall /* // The bright future: this demonstrates that // it would be fairly trivial to make some kind of annotation // like @kwarg or whaterver, to indicate that a function // was using this calling convention: @kwarg string f(int a, string b) { body; } // so that @kwarg function definitions are lowered to: struct f_kw { int a; string b; string f() { body; } } // and calls to @kwarg functions are transformed // from this: auto r = f(a=5, b="good"); // into this: f_kw tmp34; tmp34.a = 5; tmp34.b = "good"; auto r = tmp34.f(); // the benefit: named parameters can be used in a natural way, // and they need be known only at runtime. */ } // how the 'works today' above examples were implemented: struct myfunc(string init_string="") { // named keyword or named parameters // --the call arguments and their defaults int x=0; int y=0; int z=0; this(int) {} string opCall() { mixin(init_string ~ ";"); writefln("X %s, Y %s, Z %s", x, y, z ); return "yo"; } alias opCall call; }
Here's my proposal for anonymous structs that can be used as name parameters:
http://forum.dlang.org/thread/kfbnuc$1cro$1...@digitalmars.com?page=1 -- /Jacob Carlborg
