How to Efficiently Check if a Go Float64 Represents a Whole Number?

Testing Whole Number Float Equality in Go

When working with floating-point numbers in Go, it may be necessary to determine whether a given float value represents a whole number. While attempting to use the modulo operator (%) may seem like a straightforward approach, it's important to note that this operator is not defined for float64 values.

Using Integer Conversion

One approach to testing for whole number float equality is to compare the float value to a converted integer value. If the float value and the converted integer value are equal, then the float is considered a whole number. This can be achieved using the following syntax:

if a == float64(int64(a)) {
    // a is a whole number
}

Using the math.Trunc Function

For cases where the float value may exceed the range of an int64, an alternative approach is to use the math.Trunc function. This function truncates the fractional part of a float number, returning an integer value. By comparing the original float value to its truncated value, it is possible to determine if the float is a whole number:

if a == math.Trunc(a) {
    // a is a whole number
}

Example

The following Go code demonstrates the use of the math.Trunc function to correctly determine if a float value represents a whole number:

package main

import (
    "fmt"
    "math"
)

func main() {
    var a float64 = 2.00
    if a == math.Trunc(a) {
        fmt.Println("yay")
    } else {
        fmt.Println("you fail")
    }
}

In this example, the float value 2.00 is tested, and the output will be "yay" since 2.00 is a whole number.

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