Golang的早期或晚期争论评估？

Question

In my program I do a series of sequential checks in this manner:

var value int

if !(ParseOrFail(inputStrVal, &value) &&
     Validate(value)) {
    return SomeErr
}

I know that Validate is called only if ParseOrFail returns true, but I'm not sure whether in all such scenarios it will get the updated value.

Is it correct to do so? Or must I pass a pointer to Validate ?

Playground link: https://play.golang.org/p/l6XHbgQjFs

Answer 1

The Go Programming Language Specification

Expressions

An expression specifies the computation of a value by applying operators and functions to operands.

Operands

Operands denote the elementary values in an expression. An operand may be a literal, a (possibly qualified) non-blank identifier denoting a constant, variable, or function, a method expression yielding a function, or a parenthesized expression.

Order of evaluation

At package level, initialization dependencies determine the evaluation order of individual initialization expressions in variable declarations. Otherwise, when evaluating the operands of an expression, assignment, or return statement, all function calls, method calls, and communication operations are evaluated in lexical left-to-right order.

Calls

Given an expression f of function type F,

f(a1, a2, … an)

calls f with arguments a1, a2, … an. Except for one special case, arguments must be single-valued expressions assignable to the parameter types of F and are evaluated before the function is called. The type of the expression is the result type of F. A method invocation is similar but the method itself is specified as a selector upon a value of the receiver type for the method.

Logical operators

Logical operators apply to boolean values and yield a result of the same type as the operands. The right operand is evaluated conditionally.

&&    conditional AND    p && q  is  "if p then q else false"
||    conditional OR     p || q  is  "if p then true else q"
!     NOT                !p      is  "not p"

The behavior of your code is defined in The Go Programming Language Specification.

var value int

if !(ParseOrFail(inputStrVal, &value) && Validate(value)) {
    return SomeErr 
}

Or, in pseudocode,

ParseOrFail arguments are evaluated
ParseOrFail is called
if ParseOrFail == true
    Validate arguments are evaluated
    Validate is called

That is, in your example (https://play.golang.org/p/l6XHbgQjFs), late evaluation.