Re: Static assert triggered in struct constructor that shouldn't be called

[jmh530 via Digitalmars-d-learn]

On Sunday, 24 May 2020 at 21:43:34 UTC, H. S. Teoh wrote:
On Sun, May 24, 2020 at 09:34:53PM +, jmh530 via 
Digitalmars-d-learn wrote:
The following code results in the static assert in the 
constructor being triggered, even though I would have thought 
no constructor would have been called. I know that there is an 
easy fix for this (move the static if outside the 
constructor), but it still seems like it doesn't make sense.

[...]

The problem is that static assert triggers when the function is 
compiled (not when it's called), and since your ctor is not a 
template function, it will always be compiled. Hence the static 
assert will always trigger.



T


Thanks. Makes sense.

Re: Static assert triggered in struct constructor that shouldn't be called

[Adam D. Ruppe via Digitalmars-d-learn]

On Sunday, 24 May 2020 at 21:34:53 UTC, jmh530 wrote:
The following code results in the static assert in the 
constructor being triggered, even though I would have thought 
no constructor would have been called.


static assert is triggered when the code is *compiled*, whether 
it is actually run or not.


So as long s the function exists, its static asserts must all 
pass before it even gets to the runtime decision of if it is 
actually called or no.

Re: Static assert triggered in struct constructor that shouldn't be called

[H. S. Teoh via Digitalmars-d-learn]

On Sun, May 24, 2020 at 09:34:53PM +, jmh530 via Digitalmars-d-learn wrote:
> The following code results in the static assert in the constructor
> being triggered, even though I would have thought no constructor would
> have been called. I know that there is an easy fix for this (move the
> static if outside the constructor), but it still seems like it doesn't
> make sense.
[...]

The problem is that static assert triggers when the function is compiled
(not when it's called), and since your ctor is not a template function,
it will always be compiled. Hence the static assert will always trigger.


T

-- 
The trouble with TCP jokes is that it's like hearing the same joke over and 
over.

Static assert triggered in struct constructor that shouldn't be called

[jmh530 via Digitalmars-d-learn]

The following code results in the static assert in the 
constructor being triggered, even though I would have thought no 
constructor would have been called. I know that there is an easy 
fix for this (move the static if outside the constructor), but it 
still seems like it doesn't make sense.


enum Foo
{
A,
B,
}

struct Bar(Foo foo)
{
static if (foo == Foo.A)
{
float x = 0.5;
long y = 1;
}
else static if (foo == Foo.B)
{
int p = 1;
}

this(long exp, float x)
{
static if (foo == Foo.A) {
this.y = exp;
this.x = x;
} else {
static assert(0, "Not implemented");
}
}
}

void main()
{
Bar!(Foo.B) x;
}