How to Filter Go Functions Based on Parameters and Return Types Using Reflection?

Filtering Functions by Parameters and Return Types in Go

Consider a scenario where you have a collection of functions and need to selectively choose those that meet specific criteria, such as returning an integer or taking an integer as an input parameter. This task can be accomplished through the use of reflection in Golang.

The reflect package provides access to the underlying metadata of types and values in Go. By utilizing reflect.ValueOf and reflect.Type, we can inspect the function types and retrieve information about their parameters and return values.

To select functions that return an integer, we iterate through each function in the list and use reflect.ValueOf to obtain its value. We then retrieve the function's type using reflect.Type and examine its return values using NumOut and Out. If the type of any return value is "int", we mark the function as "good" for inclusion.

Similarly, to select functions that take an integer as a parameter, we iterate through the function's NumIn parameters and check the type of each input using reflect.In. If "int" is found among the input types, we mark the function as "good."

Here's an example program that demonstrates how to use this approach:

<code class="go">package main

import (
    "fmt"
    "reflect"
)

func main() {
    funcs := make([]interface{}, 3, 3)
    funcs[0] = func(a int) int { return a + 1 }
    funcs[1] = func(a string) int { return len(a) }
    funcs[2] = func(a string) string { return ":(" }

    for _, fi := range funcs {
        f := reflect.ValueOf(fi)
        functype := f.Type()
        good := false

        for i := 0; i < functype.NumIn(); i++ {
            if functype.In(i).String() == "int" {
                good = true
                break
            }
        }

        for i := 0; i < functype.NumOut(); i++ {
            if functype.Out(i).String() == "int" {
                good = true
                break
            }
        }

        if good {
            fmt.Println(f)
        }
    }
}
````
</code>

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