Is for(1) always the same as do in perl?

for(1){
  print 1;
}

do {
  print 1;
}

Is it true?

Or开发者_StackOverflow is there any special case these two doesn't equal?

---

One difference is that for(1) sets $_ to the value of 1, as well:

for(1){
    print $_;  # prints 1
}

Also, do returns the value of the last command in the sequence:

my $x = do { 1 };  # $x = 1
my $y = for(1){ 1 }; # invalid

---

You might really be looking for just plain curlies.

{
   print 1;
}

It has the following benefits:

• Creates a lexical scope (like for (1) and do {}).
• You can use next, last and redo in them (like for (1)).
• It doesn't mask $_ (like do {}).

But

• It can only used where a statement is expected (like for (1), but unlike do {}).

Therefore, { ... } makes more sense than for (1) { ... }, and do { ... } is useful when you want to return a value.

---

About the same.

• You can next, last and redo a for loop, but a do is not a loop--including as part of a do-while "loop". So in a non-trivial block, you couldn't be sure. However, this will work:

  do {{
      ...
  }};
  

• Also do will not automatically set $_ to each member of the list, the way a bare for loop will.

---

No. They have different compilation properties and have different effects. They are similar in only one dimension, that being that the code they introduce will not be looped over -- something they have in common with other constructs, including bare blocks and (sub {...})->().

Here's an obvious difference: for (LIST) BLOCK is a loop, whereas do BLOCK is an expression. This means that

for (1) {
    say "Blurgh"
} unless 1;

doesn't compile, whereas

do {
    say "Blurgh"
} unless 1;

does.