a few questions,
1| the doc on the website is not 100% clear for me.
Is it possible to have an optional const char[] argument in a static assert?
2| what am I doing wrong in the code below? Why doesn't the static
assert fire? (remark that when putting the static assert in a separate
mixin I can get it to work)


roel

======================================================================

template itoa(int n)
{
	static if (n<0)
		const char[] itoa = "-" ~ itoa!(-n);
	else static if (n<10)
		const char[] itoa = "0123456789"[n..n+1];
	else
		const char[] itoa = itoa!(n/10) ~ "0123456789"[n%10];
}

template Factor(int n:0)
{
	const int Factor = 1;
}

template Factor(int n)
{
	pragma(msg, itoa!(n));
	static assert(n>0);
	const int Factor = n * Factor!(n-1);
}


import std.stdio;
void main()
{
	writefln(Factor!(-5));
}

rm wrote:
> a few questions,
> 1| the doc on the website is not 100% clear for me.
> Is it possible to have an optional const char[] argument in a static assert?
> 2| what am I doing wrong in the code below? Why doesn't the static
> assert fire? (remark that when putting the static assert in a separate
> mixin I can get it to work)
> 
> 
> roel
> 
> ======================================================================
> 
(...)


The problem is that the order of evaluation of statements within a template instantiation is not defined. In that case, the recursion was evaluating before the static assert. One possible way to solve it:



template itoa(int n)
{
	static if (n<0)
		const char[] itoa = "-" ~ itoa!(-n);
	else static if (n<10)
		const char[] itoa = "0123456789"[n..n+1];
	else
		const char[] itoa = itoa!(n/10) ~ "0123456789"[n%10];
}

template Factor(int n:0)
{
	const int Factor = 1;
}

template next(int i) {
	static assert(i>0, "the optional const char[] argument ;) oh and by the way i = " ~ itoa!(i));
	const int next = i-1;
}

template Factor(int n)
{
	pragma(msg, itoa!(n));
	const int Factor = n * Factor!(next!(n));
}


import std.stdio;
void main()
{
	writefln(Factor!(-5));
}



--
Tomasz Stachowiak

thx,

so that the code beneath works (with the mixin),
is (bad) luck?

roel
// -----------------------------------
template Factor(int n:0)
{
	const int Factor = 1;
}

template Factor(int n)
{
	pragma(msg, itoa!(n));
//	static assert(n>0);
	mixin AssertWithMsg!(n>0,"only positive integers allowed");
	const int Factor = n * Factor!(n-1);
}

template AssertWithMsg(bool cond:false, char[] s)
{
	pragma(msg,s);
	static assert(false);
}

template AssertWithMsg(bool cond:true, char[] s)
{
}

import std.stdio;
void main()
{
	writefln(Factor!(-5));
}