How Does Short Circuit Evaluation Work in Go?

Short Circuit Evaluation in Go

In computer programming, short circuit evaluation is an optimization technique that improves the performance of conditional statements by skipping the evaluation of subsequent conditions once one condition is met. This behavior is intended to avoid unnecessary computation, especially when one condition implicitly implies the outcome of the others.

Go's Short Circuit Evaluation

Go follows the principle of short circuit evaluation. In other words, in an if statement, Go only evaluates subsequent conditions if the preceding ones are not met. This applies to both the if-else statement and the if statement without an else clause.

Performance Comparison

Let's analyze the two code snippets provided in the question:

if !isValidQueryParams(&queries) || r == nil || len(queries) == 0 {
    return "", fmt.Errorf("invalid querystring")
}

if r == nil || len(queries) == 0 || !isValidQueryParams(&queries) {
    return "", fmt.Errorf("invalid querystring")
}

In both cases, if r == nil or len(queries) == 0, the isValidQueryParams function will not be called because the overall expression is already false. Therefore, the performance optimizations may not be significant in this particular context.

Example

To demonstrate short circuit evaluation in action, consider the following code:

package main

import "fmt"

func main() {
    for i := 0; i < 10; i++ {
        if testFunc(1) || testFunc(2) {
            // do nothing
        }
    }
}

func testFunc(i int) bool {
    fmt.Printf("function %d called\n", i)
    return true
}

Running this code will print:

function 1 called
function 1 called
function 1 called
function 1 called
function 1 called
function 1 called
function 1 called
function 1 called
function 1 called
function 1 called

As you can see, the testFunc function with argument 2 is never called because the first condition (testFunc(1)) always evaluates to true. This illustrates how short circuit evaluation prevents unnecessary function calls.

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