Today I’ll be live streaming again! This time, picking up where we left off last week, and adding another feature to my new Go code rewriter and simplifier. Join me!
Order of Evaluation
…
Floating-point operations within a single expression are evaluated according to the associativity of the operators. Explicit parentheses affect the evaluation by overriding the default associativity. In the expression
x + (y + z)the additiony + zis performed before addingx.
Why bother spelling this out? Isn’t x + y + z the same as (x + y) + z the same as x + (y + z)?
Well, in mathematics, where values are precise, yes, it is. But floating point numbers are approximations, and not exact. At least not always.
Consider this simple program:
x := 0.1
y := 0.2
z := 0.3
fmt.Println(x + y + z)
fmt.Println((x + y) + z)
fmt.Println(x + (y + z))
The first two Println lines output the same value, as one might expect, since (x + y) + z follows the default order of evaluation. But the third output differs, since we override that default order. What is the output of these three lines?
0.6000000000000001
0.6000000000000001
0.6
Quotes from The Go Programming Language Specification Language version go1.22 (Feb 6, 2024)
