A friend of mine ask me why D's foreach isn't like C#

Means, why is it like
int[] arr = [1, 2, 3];

foreach (int val; arr) {

and not
foreach (int val in arr) {

which it is more intuitive.

I could give him no clever answer to, so maybe someone here knows the reasons.

On 06/29/2012 12:47 PM, Namespace wrote:
> A friend of mine ask me why D's foreach isn't like C#
> 
> Means, why is it like
> int[] arr = [1, 2, 3];
> 
> foreach (int val; arr) {
> 
> and not
> foreach (int val in arr) {
> 
> which it is more intuitive.
> 
> I could give him no clever answer to, so maybe someone here knows the reasons.
> 

I suppose it is because the usual 'for' loop is a relative of 'foreach'. And there we (and the C world) uses ';'.

Namespace:
> A friend of mine ask me why D's foreach isn't like C#

In D you often omit the type:

foreach (val; arr) {

Using "in" is better for the human programmers. But D is largely designed to make D compilers too happy. I think Walter said that the semicolon was preferred because it simplifies the compiler/compilation a little.

Bye,
bearophile

On Fri, 29 Jun 2012 12:47:28 +0200, Namespace wrote:

> A friend of mine ask me why D's foreach isn't like C#
> 
> Means, why is it like int[] arr = [1, 2, 3];
> 
> foreach (int val; arr) {
> 
> and not foreach (int val in arr) {
> 
> which it is more intuitive.
> 
> I could give him no clever answer to, so maybe someone here knows the reasons.


Because
1) "in" is a D keyword
2) D has even shorter syntax: foreach(val; arr) {}


-- 
Dejan Lekic
  mailto:dejan.lekic(a)gmail.com
  http://dejan.lekic.org

On 06/29/2012 12:47 PM, Namespace wrote:
> A friend of mine ask me why D's foreach isn't like C#
>
> Means, why is it like
> int[] arr = [1, 2, 3];
>
> foreach (int val; arr) {
>

foreach(val; arr) {

> and not
> foreach (int val in arr) {
>
> which it is more intuitive.
>

To someone coming from C#, yes.

> I could give him no clever answer to, so maybe someone here knows the
> reasons.

Just because. This does not matter.

Timon Gehr:

> Just because. This does not matter.

Now and then I write foreach(x;y;data) or foreach(x,y,data) or foreach(x;y,data). "in" avoids some of those little mistakes.

Bye,
bearophile

On 06/29/2012 01:01 PM, bearophile wrote:
> Namespace:
>> A friend of mine ask me why D's foreach isn't like C#
>
> In D you often omit the type:
>
> foreach (val; arr) {
>
> Using "in" is better for the human programmers.

Certainly not. (except if 'human' means 'python' or 'C#'.)
It is just as good as ';'.

> But D is largely
> designed to make D compilers too happy. I think Walter said that the
> semicolon was preferred because it simplifies the compiler/compilation a
> little.

It does not. Parsing the statements just about the same. In fact, only
2 lines in the DMD parser implementation need to be changed (slightly!)
to implement the 'in' syntax instead.

On 06/29/2012 04:16 PM, bearophile wrote:
> Timon Gehr:
>
>> Just because. This does not matter.
>
> Now and then I write foreach(x;y;data)

error: found ';' when expecting ')'

> or foreach(x,y,data) or

error: found ')' when expecting ';'

> foreach(x;y,data).

error: undefined identifier y

> "in" avoids some of those little mistakes.
>

foreach(x in y,data)

On 06/29/2012 04:23 PM, Timon Gehr wrote:
> ...
>> foreach(x;y,data).
>
> error: undefined identifier y
>

BTW, it would certainly be better if this didn't actually pass the parser.

Timon Gehr:

> foreach(x in y,data)

There is no way to avoid all possible mistakes, but it's easier to mistake a ";" for a ",", than mistake a "in" for a ",".

"in" is used for this purpose in Python, C#, and probably other languages because it's more readable than an arbitrary symbol like ";".

Bye,
bearophile