Bug #15616: Chained destructive methods fail when using +@ to unfreeze a frozen string

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: 2.6.1
• Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN

[cianooooo (Cian O)]

Using the +@ syntax to unfreeze a string does not work when chaining destructive methods

Consider the following;

foo = "bar".freeze
+foo.gsub!("bar", "car")

This raises;

FrozenError: can't modify frozen String

However, I would have expected this to work since +@ should return a duplicated mutable string.

[ahorek (Pavel Rosický)]

+foo.gsub!("bar", "car")

stands for

+(foo.gsub!("bar", "car"))

and because foo is frozen, you'll get an error, see #15606

try this

foo = "bar".freeze
foo = (+foo).gsub!("bar", "car")

or

foo = "bar".freeze
foo = foo.gsub("bar", "car")

[duerst (Martin Dürst)]

• Status changed from Open to Rejected

Yes. It's a matter of precedence. The "Pickaxe" book describes it as

Single terms in an expression may be any of the following:

[some cases omitted]

• Method invocation

That means that in +foo.gsub!("bar", "car"), the . of method invocation has higher precedence than the +, and so you need to use parentheses if you want to change the order of evaluation.