[ruby-core:86320] [Ruby trunk Bug#14624] #{nil} allocates a fresh empty string each time

Issue #14624 has been updated by bumblingbear (Dillon Welch).


Closer to the string interpolation optimization part. The problem with "#{nil}" is that it allocates two empty strings each time. I feel like it would be possible to do this with zero/one allocation. I don't know what the underlying code looks like, but the logic I'm thinking of is something like
```
def interpolate(obj)
  if obj == nil
    ''
  else 
    obj.to_s # assuming this is current behavior
  end
end
```

phluid61 (Matthew Kerwin) wrote:
> I'm confused; are you proposing that `nil.to_s` returns the same String object every time, or that string interpolation detects a `nil` object and optimises it?
> 
> A lot of times I rely on `"#{foo}"` returning a new String object that contains a copy of the #to_s of `foo`, so it seems to me like spec that `"#{nil}"` returns a new empty string every time.



----------------------------------------
Bug #14624: #{nil} allocates a fresh empty string each time
https://bugs.ruby-lang.org/issues/14624#change-71239

* Author: bumblingbear (Dillon Welch)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
This causes a bunch of unnecessary string allocations in the following scenario: "#{'rails' unless boolean_condition} is great". Each time this line is called when boolean_condition is true, it evaluates to nil and when nil is interpolated into a string it allocates an empty string. Ideally, the behavior of nil.to_s would reference a frozen empty string that wouldn't need to be reallocated each time.



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