Re^2: Nested Hash Dereferencing Syntax

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Re^3: Nested Hash Dereferencing Syntax by tilly (Archbishop) on Feb 24, 2009 at 18:19 UTC
Here is an explanation of why parens cannot be used there. If you could write `%($hash{$key})` then you should expect to be able to write `%($hash{$key}){$other_key}`. But perlvar tells us that $( is a built-in special variable, so correctly knowing how to parse that would be very, very hard. Incidentally %( is a valid Perl hash, though it is not used for anything and accessing it can get tricky. But the following is valid Perl: `%( = 0..9; print keys(%();` [download]	[reply] [d/l] [select]
Re^4: Nested Hash Dereferencing Syntax by ikegami (Patriarch) on Feb 24, 2009 at 18:31 UTC
I thought of that, but dismissed it. He could have named `$(` something different if he wanted to use parens for variables, or did `"${var}"` come later? I figured it had been in Perl from the start due to its parallel in bourne.	[reply] [d/l] [select]
Re^5: Nested Hash Dereferencing Syntax by tilly (Archbishop) on Feb 24, 2009 at 21:21 UTC
I agree that ${...} is certainly originally in Perl because of the familiarity of the syntax in shell. But Perl is willing to change syntax if a new one is clearer - witness the switch from ' to :: as a package separator. But my understanding is that references and most of our dereferencing syntax was added in Perl 5. Which means that backwards compatibility would prevent the $(...) syntax from being introduced after that.	[reply]
Re^3: Nested Hash Dereferencing Syntax by chromatic (Archbishop) on Feb 24, 2009 at 19:03 UTC
Do you know why curlies, and not parens, are necessary here? Because parentheses only ever group things, never performing any nesting or scoping or accessing.	[reply]
Re^3: Nested Hash Dereferencing Syntax by ikegami (Patriarch) on Feb 24, 2009 at 17:38 UTC
No, I don't know why. Curlies are always used where are variables name is expected. `my $x = ${$hash_ref}{key}; # Original syntax my $x = $hash_ref->{key}; # Newer, cleaner syntax print($foo, "bar\n"); print("${foo}bar\n"); # same print("$foobar\n"); # XXX my $x = ${"varname"}; # Symbolic reference` [download] etc.	[reply] [d/l]
Re^3: Nested Hash Dereferencing Syntax by Bloodnok (Vicar) on Feb 24, 2009 at 18:11 UTC
It strikes me that curlies (or braces) are used for legacy reasons given that the provenance of the language is the NIX shell (see, to name but one, Perl). As we all know, NIX shell uses braces in references to environment variables - when and only when the variable isn't followed by a printable, non-word boundary char can the braces be omitted e.g. `${foo}_bar` is the var `foo` with _bar appended, whereas `$foo_bar` refers to a variable named `foo_bar`. This (string interpolation) is true for both shell and perl, but interestingly (I really ought to get out more:-) not in `make(1)` scripts - which can take braces or parens as separators. Update: Thanx to tilly for the hint. A user level that continues to overstate my experience :-))	[reply] [d/l] [select]
Re^4: Nested Hash Dereferencing Syntax by tilly (Archbishop) on Feb 24, 2009 at 18:24 UTC
I don't understand what you mean by saying that Perl is like shell in this regard unless you are talking about string interpolation.	[reply]