• Baby Beaker (1/1) May 03 2020 How can I assign a variable in “if” condition in Dlang?
• H. S. Teoh (8/9) May 03 2020 if (auto obj = someFunction(...)) {
• kdevel (28/35) May 03 2020 What if someFunction's return type is string? I mean this:
• Steven Schveighoffer (4/11) May 03 2020 Then you have to do it in 2 steps. It would be nice to have a way to do
• Adam D. Ruppe (4/5) May 03 2020 depends on exactly what there's also
• Steven Schveighoffer (3/11) May 03 2020 That doesn't work. You need to do a comparison or a cast.

Baby Beaker <thegrapevine email.com> writes:

How can I assign a variable in “if” condition in Dlang?

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Sun, May 03, 2020 at 02:53:21PM +0000, Baby Beaker via Digitalmars-d-learn
wrote:
 How can I assign a variable in “if” condition in Dlang?

	if (auto obj = someFunction(...)) {
		// use obj here, it's guaranteed to be
		// true/non-null/etc.
	}


T

-- 
EMACS = Extremely Massive And Cumbersome System

kdevel <kdevel vogtner.de> writes:

On Sunday, 3 May 2020 at 15:13:48 UTC, H. S. Teoh wrote:
 On Sun, May 03, 2020 at 02:53:21PM +0000, Baby Beaker via 
 Digitalmars-d-learn wrote:
 How can I assign a variable in “if” condition in Dlang?

 	if (auto obj = someFunction(...)) {
 		// use obj here, it's guaranteed to be
 		// true/non-null/etc.
 	}

What if someFunction's return type is string? I mean this:

```if.d
void eval (string function () fun)
{
    import std.stdio;
    if (auto s = fun ())
       "true".writeln;
    else
       "false".writeln;
}

void main ()
{
    () { string s; return s; }.eval;       // empty string
    () { string s = ""; return s; }.eval;  // empty string
}
```

It surprisingly [1] [2] prints:

    false
    true

In the string case there is at least not the guarantee that the 
string is non-empty.

[1] Empty string vs null
     
https://forum.dlang.org/thread/fehvcobsjuklxynbqqox forum.dlang.org

[2] The Nullity Of strings and Its Meaning
     
https://forum.dlang.org/thread/qcmtjfpkvcoyvrouvccw forum.dlang.org

Steven Schveighoffer <schveiguy gmail.com> writes:

On 5/3/20 12:30 PM, kdevel wrote:
 It surprisingly [1] [2] prints:
 
     false
     true
 
 In the string case there is at least not the guarantee that the string 
 is non-empty.

Then you have to do it in 2 steps. It would be nice to have a way to do 
this, but there isn't right now.

-Steve

Adam D. Ruppe <destructionator gmail.com> writes:

On Sunday, 3 May 2020 at 14:53:21 UTC, Baby Beaker wrote:
 How can I assign a variable in “if” condition in Dlang?

depends on exactly what there's also

if ( (a = 10) )

with extra parens for special purposes

Steven Schveighoffer <schveiguy gmail.com> writes:

On 5/3/20 11:27 AM, Adam D. Ruppe wrote:
 On Sunday, 3 May 2020 at 14:53:21 UTC, Baby Beaker wrote:
 How can I assign a variable in “if” condition in Dlang?

 
 depends on exactly what there's also
 
 if ( (a = 10) )
 
 with extra parens for special purposes

That doesn't work. You need to do a comparison or a cast.

-Steve