Better assert without changing built-in assert

[Jim]

Jens Mueller Wrote:

> Hi,
> 
> I'm trying to improve the assertions. I tried the following
> auto foo(bool var) {
> 	return tuple(var, "MyMessage");
> }
> 
> void bar(bool var, string text) {
> }
> 
> unittest {
> 	bar(foo(true).expand);
> 	//assert(foo(true).expand); // won't compile
> }
> 
> void main() {}
> 
> $ dmd -unittest -run file.d
> Commenting in the assert it fails with
> "Error: expression
> tuple(foo(true)._field_field_0,foo(true)._field_field_1) of type (bool,
> string) does not have a boolean value"
> 
> assert behaves different when expanding tuples. Any explanations?
> If one could do the above without writing the expand then it would
> suggest a nice way of enhancing the build-in assert, I think.
> If one cannot make it work without the .expand another option may be
> to overload the built-in assert to handle tuples. This may be related to
> http://d.puremagic.com/issues/show_bug.cgi?id=5547
> Then one writes e.g.
> assert(throws!MyException(expression))
> or
> assert(pred!("==")(a, b))
> What do you think?
> 
> Jens


Or like this:


import std.conv;

string cat(T...)(T ts)
{
	string s;
	foreach(t; ts)
	 s ~= to!string(t) ~ " ";
	return s;
}


unittest
{
	...
	assert(a==b, cat(a,b));
}