add with compound statement

[WalterBright]

This was requested in the newsgroups. Adds the syntax:

{
    with (E):
       statement;
       statement;
}

which is equivalent to:

{
    with (E)
    {
       statement;
       statement;
    }
}

[dlang-bot]

Thanks for your pull request, @WalterBright!

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[WalterBright]

Spec PR dlang/dlang.org#4163

[ibuclaw]

Note, these are accepted at global, but rejected at a scope level.

void example()
{
    { version(all): int decl; }
    { static if(cond): int decl; }
}   

Where does this sit with other kinds of statements that have ScopeStatement bodies, which don't get the same syntactical sugar treatment?

{
  if (cond):
    statement;
    statement;
}
{
  while (cond):
    statement;
    statement;
}
{
  do:
    statement;
    statement;
  while (cond);
}
{
  for (elem; list):
    statement;
}
{
  foreach (elem; list):
    statement;
}
{
  synchronized (object):
    statement;
}
{
  try:
    statement;
  catch (type):
    statement;
  finally:
    statement;
}
{
  switch (cond):
    case 1:
      break;
    default:
      break;
}

[WalterBright]

A fair question. It only came up in the n.g. as a convenience wish for with. We also started with if (declaration), which was eventually generalized to switch (declaration), etc., once it proved its desirability. We can start with with: and see how it goes.

[nordlow]

I have also been longing for allowing similar syntax for pragma(...) in my case specifically for

pragma(inline):
pragma(inline, false):
pragma(inline, true):

.

Is this possible to add support for?

[thewilsonator]

pragma(ident): // influence subsequent declarations
    declaration;
    declaration;

https://dlang.org/spec/pragma.html That already works.

[nordlow]

https://dlang.org/spec/pragma.html That already works.

Ahh. I forgot. Sorry for disturbing. Thanks.

[ghost]

commit message should be updated so that #17700 will close

[Geod24]

This is the kind of change that @deadalnix will complain about because it will break tooling and force them to implement this new syntax. The question is, is it worth it ? Personally I don't think so. Using : is not, IMO, a good experience for version, as it expands the scope a programmer needs to look at to understand the code. Especially with with statement as they can affect multiple parts of a line in a non-obvious manner.

[p0nce]

Personally love this, I've often reached out for with(ident): before

[Bolpat]

Syntax-wise, : is unheard of (except for labels). I’d rather use with AssignExpression; ― compare:

void main()
{
    with (x):
        statement;
}

and

void main()
{
    with x;
    statement;
}

It would work similar to C#’s using statement which is

• either using (ExpressionOrDeclaration) { … }
• or using Declaration;.

If we’re at it, with should allow a declaration in that form:

with Object o = new Exception;
auto str = toString(); // auto str = o.toString()

Requiring auto x = …; with x; would be annoying.

[thewilsonator]

: appears in that fashion (enclose the following in a scope until end of current scope) in the grammar in at least

• @attribute: (including pure, nothrow)
• static if:
• pragma(foo):

[Bolpat]

: appears in that fashion (enclose the following in a scope until end of current scope)

That is true for declaration scope only. It is expressly not true for statement scope in D and across languages.