Break out of a begin/end block early

I want a way to exit a begin/end block while still assigning the variable that its result is assigned to.

def foo
  @foo ||= begin
    puts "running"

    return "leaving early" if true # would be some sort of calculation

    # Other calculations
  end
end

What I hope to happen

> foo
running
=> leaving early
> foo
=> leaving early

What actually happens

> foo
running
=> leaving early
> foo
running
=> leaving early

The code doesn't work because return exits the entire method without setting @foo. Using break or next only work in loops. Does anything work within a begin block the way I'm thinking?

Current ways I can do it but was hoping to avoid:

Assigning the variable within the begin block and returning
Putting the remaining portion of the begin block in an if statement
Performing the calculation before the begin block

There seem to be a lot of related questions about breaking out of blocks but I couldn't find one that answers this specific version (maybe because it's not possible).

Solution

I think you're going to save yourself a whole heck of a lot of strife if you just put all that logic into its own method:

def foo
  @foo ||= compute_foo
end

def compute_foo
  puts "running"

  return "leaving early" if true # would be some sort of calculation

  # Other calculations
end

This decouples the computation from the memoization, making it easier to test and reason about, and it's a fairly common design pattern in Ruby and other languages.

Of course, there are ways of doing what you're asking. The most obvious solution being an immediately-invoked anonymous proc:

def foo
  @foo ||= (proc do
    puts "running"

    next "leaving early" if true # would be some sort of calculation

    # Other calculations
  end)[] # or .call or .()
end

But you certainly wouldn't be doing yourself or any future maintainers of this code any favors.