584957 - Broken Increment Behavior

Status: RESOLVED INVALID

(Core :: JavaScript Engine, defect)

Description

[Sean Stangl [:sstangl]]

While debugging bug 584651, I stumbled upon the following interesting behavior in the interpreter. Consider the following statements:

function a(x) { print(x) };

x = 5;
a(x++) => prints "5"
print(x) => prints "6"

Now consider, with the same definition of 'a':

x = Math.pow;
a(x++) => prints "NaN"
print(x) => prints "NaN"

The latter "a(x++)" should print out a native code object. We appear to be incrementing too early.

Comment 1

[Brendan Eich [:brendan]]

See ES5 11.3.1 Postfix Increment Operator step 3 and 6, or equivalent in previous editions:

3. Let oldValue be ToNumber(GetValue(lhs)).
. . .
6. Return oldValue.

/be