Strange template problem

[Kirk McDonald]

Tom S wrote:
> Kirk McDonald wrote:
> 
>> I'm having some trouble with a very odd template problem. Take the 
>> following code:
>>
>> [test.d]
>> import std.stdio;
>> import ftype; // Daniel Keep's ftype module
>>
>> // A function with default arguments
>> void foo(int i=20, char[] s="Monkey") {
>>     writefln("foo: %s %s", i, s);
>> }
>>
>> // A function with the same arguments and no defaults
>> void bar(int i, char[] s) {
>>     writefln("bar: %s %s", i, s);
>> }
>>
>> // A function that takes a function pointer and the minimum
>> // number of arguments the function can be called with, and
>> // calls it.
>> void Baz(fn_t, uint MIN_ARGS)(fn_t fn) {
>>     static if (MIN_ARGS == 0)
>>         fn();
> 
> 
> MIN_ARGS is 0 for 'foo', because thats what the NumberOfArgs template 
> returns, using the function *alias*. the *type* doesnt tell the compiler 
> that it can be called with no args. thats just a func type that takes 
> two args. thus the error.

Then why does it work when I comment out line 28?

> 
> 
>>     else static if (MIN_ARGS == 1)
>>         fn(10);
>>     else static if (MIN_ARGS == 2)
>>         fn(15, "Copper");
>> }
>>
>> // A template function that takes a function alias and the
>> // minimum number of args it can be called with, and calls
>> // Baz
>> void Blah(alias Fn, uint MIN_ARGS = NumberOfArgs!(typeof(&Fn))) () {
>>     alias typeof(&Fn) fn_t;
>>     fn_t fn = &Fn;
>>     Baz!(fn_t, MIN_ARGS)(fn);
>> }
>>
>> void main() {
>>     Blah!(bar);    // Line 28
>>     Blah!(foo, 0); // Line 29
>> }
>>
>> $ build test
>> test.d(14): Error: expected 2 arguments, not 0
>>
>> test.d(24): template instance test22.Baz!(void(*)(int i, char[] s),0u) 
>> error instantiating
>> test.d(29): template instance test22.Blah!(foo,0) error instantiating
>>
>> Curiously, this works if I comment out line 28:
>>
>> $ build test
>> gcc test.o ftype.o -o test -m32 -lphobos -lpthread -lm
>> $ ./test
>> foo: 20 Monkey
>>
>> It also works if I comment out line 29 instead:
>>
>> $ build test
>> gcc test.o ftype.o -o test -m32 -lphobos -lpthread -lm
>> $ ./test
>> bar: 15 Copper
>>
>> But if both lines are there together, it fails.
>>
> 
> 


-- 
Kirk McDonald
Pyd: Wrapping Python with D
http://dsource.org/projects/pyd/wiki