Official expansion of ||= conditional assignment operator

Question

I want to emphasize I am looking for the actual way the ||= operator is expanded by the Ruby 1.9.3 interpreter, not how it appears to be expan

Answer 1

EDIT: This post is about the spec, read the comments to get the somewhat less ideal "implementation story"

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The Ruby draft spec (PDF) section 11.4.2.3.2 defines it fairly specifically (even if fairly hard to interpret); let's do a (theoretically somewhat loose) example with c ||= 3;

a) Evaluate the variable as a variable reference (see 11.5.4). Let V be the resulting value.

V is set to the value of c

b) Evaluate the operator-expression or the method-invocation-without-parentheses. Let W be the resulting value.

W is set to 3.

c) Let OP be the assignment-operator-name of the assignment-operator.

OP is set to ||

d) Let X be the operator-expression of the form V OP W.

X is set to c || 3.

e) Let I be the variable of the abbreviated-variable-assignment-expression or the abbreviated- variable-assignment-statement.

I is set to refer to c.

f) Evaluate a single-variable-assignment-expression (see 11.4.2.2.2) where its variable is I and the operator-expression is X.

c = c || 3 is evaluated.

g) The value of the abbreviated-variable-assignment is the resulting value of the evaluation.

The result of the assignment is 3.

In other words, the expansion c = c || 3 is (excluding bugs like in pre-1.9) correct.