Is a Foreach loop a type of block?

Question

In thinking about blocks, I've always wondered why the

thingers.each { |thing|

example is actually interesting (since there's another, built-in way to do it). In most modern languages there's a way to iterate through a collection and apply some inline code to it. But then I thought that maybe the for (Thing thing : things) { syntax is really a type of block, even in languages like Java-sans-Groovy where there are none.

So the question is: Is a for-each loop a type of block, albeit with a fixed syntax?

Edit: This question is confusing but yet got some attention so I can't delete it. Anyway... by Blocks I mean "closures" and not just code blocks. As far as why I tagged this as language agnostic is that I'm not interested in how a for-each is implemented under-the-hood. I'm more interested in whether, from a programmer's perspective, a for-each could be considered a freebie closure in languages that doesn't have them, like Java.

Answer 1

Please elaborate. My definition of a "block" is a section of code that's grouped together. In this case there's a lot of stuff in Java can be a "block"

If you are talking about ruby-style blocks, which are really closures, then Java doesn't support them (not in any sane fashion anyways). foreach is a control structure, and behaves differently from closures.

On your updated question: It's easy to use closures as control structures, but the other way around is harder, if not impossible. A closure is a first class function, which allows you to do some pretty cool stuff with it - not just iterating through elements.

Answer 2

This is most definitely not language agnostic (as it is tagged).

For example, in Ruby, you are passing a closure or block to the .each method. The semantics are defined by the language.

In C#, foreach compiles to a call to IEnumerable.GetEnumerator and the use of the IEnumerator.MoveNext method. It just depends on the language.

EDIT:

Edit: This question is confusing but yet got some attention so I can't delete it. Anyway... by Blocks I mean "closures" and not just code blocks. As far as why I tagged this as language agnostic is that I'm not interested in how a for-each is implemented under-the-hood. I'm more interested in whether, from a programmer's perspective, a for-each could be considered a freebie closure in languages that doesn't have them, like Java.

No, you are thinking only of one use case for a closure. You can't pass a control structure to a method as you can a closure in some languages. A control structure is not a first class first class data type like a closure is in some languages. In the case of "run this code on each object in a collection" yes, they are semantically similar. However, that it only one example of what you can do with a closure.

You say that you w

Answer 3

As Swangren says, this question is not language agnostic as tagged. Not unless there's some general "IT theory" definition of a "block" that I'm not aware of.

In Java, a "block" is a series of statements enclosed in { }. So a FOR statement normally operates on a block. The purpose of a block is to delimit what is included within certain language constructs, like IF statements and loops.

I believe C and C++ have similar definitions of a "block".

Most languages have a similar concept.

Not sure if this helps.

Answer 4

foreach ($foo as $bar) {
    $baz = 'Hello, World!';
}

echo $baz; // 'Hello, World!', "leaked" from the "closure"

Nope, sorry, foreach loops are not lambdas, closures or functions in languages where they aren't explicitly such.