Variable references in strings (Was: Structs implementing interfaces in D1)

[Ary Borenszweig]

Tom S escribió:
> /** Just a simple hack to have interfaces implemented by structs ... 
> because I can :P
> Tested on DMD 1.039 [win32], GDC (various versions) [linux32] and 
> codepad.org
> 
> Output:
> 
> Entering main
> Foo.func1 called ; val1 = 3.141590, val2 = Hello, world!
> Foo.func2 called ; val1 = 3.141590, val2 = Hello, world!
> Foo.func2 called ; val1 = 3.141590, val2 = Hello, world!
> Foo.func3 called ; val1 = 3.141590, val2 = Hello, world! ; p1 = 123, p2 
> = some parameter
> Leaving main
> */
> 
> 
> module structIface;
> 
> extern (C) int printf(char*, ...);
> 
> 
> 
> // ---- evil implementation
> char[] structImplementInterface(char[] iface, char[][] funcs) {
>     char[] res = "private {";
>     res ~= \n"alias typeof(*this) _iface_"~iface~"_ThisType;";
> 
>     foreach (func; funcs) {
>         res ~= \n"static assert (is(typeof(&"~iface~".init."~func~")),
>             `The interface "~iface~" doesn't declare a '"~func~"' 
> function, `
>             `thus struct `~_iface_"~iface~"_ThisType.stringof~` cannot 
> implement it`);";
>         res ~= \n"static void _iface_" ~ iface ~ "_func_" ~ func ~ "() {";
>         version (GNU) {
>             res ~= \n\t"asm { naked; sub dword ptr 4[ESP], _iface_" ~ 
> iface ~ "_vtbl.offsetof; jmp " ~ func ~ "; }";
>         } else {
>             res ~= \n\t"asm { naked; sub EAX, _iface_" ~ iface ~ 
> "_vtbl.offsetof; jmp " ~ func ~ "; }";
>         }
>         res ~= \n"}";
>     }
>     res ~= \n ~ iface ~ " as" ~ iface ~ "() {";
>     res ~= \n\t"return cast("~iface~")cast(void*)&_iface_" ~ iface ~ 
> "_vtbl;";
>     res ~= \n"}";
> 
>     res ~= \n"void** _iface_" ~ iface ~ "_vtbl = cast(void**)([";
>     res ~= \n\t"null";        // for classinfo
>     foreach (func; funcs) {
>         res ~= ",\n\tcast(void*)&Foo._iface_" ~ iface ~ "_func_" ~ func;
>     }
>     res ~= \n"]).ptr;";
>     res ~= "}";
> 
>     return res;
> }
> // ---- end of the evil implementation

Since a lot of compile stuff is done via strings, I wish you could do 
somehing like this in D (like in PHP):

res ~= res ~= "\n\treturn cast(${iface})cast(void*)&_iface_${iface}_vtbl;";

Much nicer and understandable. And I think it's not hard to implement: 
when doing semantic for a string like that, parse it and search the 
variables in the current scope and upwards (as a usual search). For this 
to work, primitives should have a string representation, and if it's a 
class or struct, then toString() is invoked.

It's really hard to follow a code like that, with thousands of "~".

And maybe this should only be done for strings enclosed in `, so that 
the search is not always done.