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digitalmars.D.learn - Make foreach element optional

reply Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
I find myself writing

foreach (_; 0 .. n)
     doSomething(); // no using the variable `_`

.

What about relaxing the syntax to allow

     foreach (; 0 .. n)

and/or

     foreach (0 .. n)

?

Thereby making the `ForeachTypeList` of `AggregateForeach` in the 
grammar rule [1] optional.

[1] https://dlang.org/spec/statement.html#foreach-statement
Mar 16 2021
next sibling parent reply Imperatorn <johan_forsberg_86 hotmail.com> writes:
On Tuesday, 16 March 2021 at 12:49:13 UTC, Per Nordlöw wrote:

 I find myself writing

 foreach (_; 0 .. n)
     doSomething(); // no using the variable `_`

 .

 What about relaxing the syntax to allow

     foreach (; 0 .. n)

 and/or

     foreach (0 .. n)

 ?

 Thereby making the `ForeachTypeList` of `AggregateForeach` in 
 the grammar rule [1] optional.

 [1] https://dlang.org/spec/statement.html#foreach-statement


foreach(0..n) could work. Why though.
Mar 16 2021
parent reply Per =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
On Tuesday, 16 March 2021 at 13:31:34 UTC, Imperatorn wrote:

 foreach(0..n) could work. Why though.


When performing a side-effect n times.
Mar 16 2021
parent reply Imperatorn <johan_forsberg_86 hotmail.com> writes:
On Tuesday, 16 March 2021 at 13:52:29 UTC, Per Nordlöw wrote:

 On Tuesday, 16 March 2021 at 13:31:34 UTC, Imperatorn wrote:

 foreach(0..n) could work. Why though.


 When performing a side-effect n times.


Then why not just do:

auto times(alias F, T)(T number)
{
     return number.iota.each!(_ => F());
}

void f()
{
     writeln("hi");
}

n.times!(f);

?
Mar 16 2021
parent bachmeier <no spam.net> writes:
On Tuesday, 16 March 2021 at 16:29:45 UTC, Imperatorn wrote:

 On Tuesday, 16 March 2021 at 13:52:29 UTC, Per Nordlöw wrote:

 On Tuesday, 16 March 2021 at 13:31:34 UTC, Imperatorn wrote:

 foreach(0..n) could work. Why though.


 When performing a side-effect n times.


 Then why not just do:

 auto times(alias F, T)(T number)
 {
     return number.iota.each!(_ => F());
 }

 void f()
 {
     writeln("hi");
 }

 n.times!(f);

 ?


To my knowledge, there's nothing like this in the standard 
library or the language. I used something similar but eventually 
decided it was simpler to use the original foreach. It'd honestly 
have to be a language change to be useful. (Given the benefit, I 
doubt this would happen.)
Mar 16 2021
prev sibling next sibling parent reply Steven Schveighoffer <schveiguy gmail.com> writes:
On 3/16/21 8:49 AM, Per Nordlöw wrote:

 I find myself writing
 
 foreach (_; 0 .. n)
      doSomething(); // no using the variable `_`
 
 .
 
 What about relaxing the syntax to allow
 
      foreach (; 0 .. n)
 
 and/or
 
      foreach (0 .. n)
 
 ?
 
 Thereby making the `ForeachTypeList` of `AggregateForeach` in the 
 grammar rule [1] optional.
 
 [1] https://dlang.org/spec/statement.html#foreach-statement


Meh, is this a common need though? The first form isn't terrible.

In general, I'd say it would be nice to designate _ as an unused 
variable (i.e. not allowed to access it, and it doesn't trigger 
shadowing errors). It's like this in Swift for instance.

-Steve
Mar 16 2021
parent Jack <jckj33 gmail.com> writes:
On Tuesday, 16 March 2021 at 15:02:54 UTC, Steven Schveighoffer 
wrote:

 On 3/16/21 8:49 AM, Per Nordlöw wrote:

 I find myself writing
 
 foreach (_; 0 .. n)
      doSomething(); // no using the variable `_`
 
 .
 
 What about relaxing the syntax to allow
 
      foreach (; 0 .. n)
 
 and/or
 
      foreach (0 .. n)
 
 ?
 
 Thereby making the `ForeachTypeList` of `AggregateForeach` in 
 the grammar rule [1] optional.
 
 [1] https://dlang.org/spec/statement.html#foreach-statement


 Meh, is this a common need though? The first form isn't 
 terrible.

 In general, I'd say it would be nice to designate _ as an 
 unused variable (i.e. not allowed to access it, and it doesn't 
 trigger shadowing errors). It's like this in Swift for instance.

 -Steve


the _ as unused variable would be useful when the parameter has 

this currently.

int foo(int x, out bool state) { }

// only wants return value
int y = foo(x, _);
Mar 16 2021
prev sibling parent bachmeier <no spam.net> writes:
On Tuesday, 16 March 2021 at 12:49:13 UTC, Per Nordlöw wrote:

 I find myself writing

 foreach (_; 0 .. n)
     doSomething(); // no using the variable `_`

 .

 What about relaxing the syntax to allow

     foreach (; 0 .. n)

 and/or

     foreach (0 .. n)

 ?

 Thereby making the `ForeachTypeList` of `AggregateForeach` in 
 the grammar rule [1] optional.

 [1] https://dlang.org/spec/statement.html#foreach-statement


The gain to altering the foreach statement is minimal since _ is 
a nice convention to use if you don't need the value of the 
counter.

Something like this gives cleaner code:

replicate(100) {
   // do stuff with side effects
}

I don't know if it would be an opportunity for a compiler 
optimization (probably not).
Mar 16 2021