IEnumerable is eagerly iterated

Writing a for loop over IEnumerable objects works but it seems like it enumerates everything (supposedly in an array buffer?) before executing any loop body and performing rendering.

As a user, this is surprising as the similar foreach goes through the enumerable lazily.

It has some undesirable consequences:

When the template code influences the enumeration itself. This is my use-case and how I noticed this: I have a queue of items that needs to be rendered, and rendering one item can enqueue a new one. Anything enqueued inside the loop isn’t processed.

Processing infinite sequences is impossible. You may be tempted to do a TakeWhile pattern but it won’t work:

for item in infinite
  if item.stop_here; break; end
end

[xoofx]

Fixed by commit b39f7a1, will be available in next version

[xoofx]

Agreed, it was introduced quite some time ago because Liquid was requiring the length to be accessible in a variable, so I made quite some change back in the days (the previous implementation was much simpler actually)

https://github.com/scriban/scriban/blob/3ba3cc3ec8baa65a3a5983c1e610ad5cfc662b5f/src/Scriban/Syntax/Statements/ScriptForStatement.cs#L114-L116

So rethinking about it, it should be possible to make the access of the length deferred (so that in that case you pay the price of a potential forced iteration on all elements) and use the enumeration otherwise for the loop.