Issue #8579 has been updated by kstephens (Kurt  Stephens).


How about something more generic?  A prefix operator that memoizes and freezes any expression result in a thread-safe manner on first eval:

    %f'a frozen string'                 #
    %f"a frozen #{interpolated} string" # 
    %f{a: 'frozen', :hash 'value'}      # A frozen, inline memoized Hash.
    %f[:a, 'frozen', :array, 'value']   # A frozen, inline, memoized Array.
    %f(some(:method, 'call'))           # You get the idea.

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Feature #8579: Frozen string syntax
https://bugs.ruby-lang.org/issues/8579#change-41341

Author: charliesome (Charlie Somerville)
Status: Open
Priority: Normal
Assignee: ko1 (Koichi Sasada)
Category: syntax
Target version: current: 2.1.0


I'd like to propose a new type of string literal - %f().

Because Ruby strings are mutable, every time a string literal is evaluated a new String object must be duped.

It's quite common to see code that stores a frozen String object into a constant which is then reused for performance reasons. Example: https://github.com/rack/rack/blob/master/lib/rack/methodoverride.rb

A new %f() string literal would instead evaluate to the same frozen String object every time. The benefit of this syntax is that it removes the need to pull string literals away from where they are used.

Here's an example of the proposed %f() syntax in action:

    def foo
      ["bar".object_id, %f(bar).object_id]
    end

    p foo # might print "[123, 456]"

    p foo # might print "[789, 456]"

These string literals could also be stored into a global refcounted table for deduplication across the entire program, futher reducing memory usage.

If this proposal is accepted, I can handle implementation work.


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