assignment mismatch 1 variable but fmt.println returns 2 values

Go by Example : Multiple Return Values

Next example: Variadic Functions .

by Mark McGranaghan and Eli Bendersky | source | license

Functions in Golang

Gurleen Sethi on 01 May 2022

Getting Started #

Functions are at the core of Golang , they are easy to understand, fun to work with and surprisingly provide a decent amount of flexibility. In this article I aim to teach you the main aspects of functions.

As always, I recommend you to try out all the examples by hand 👨🏻‍💻 the more you practice, the more you understand, and the more you retain. Go Playground and GoPlay are good online websites to quickly write and run some go code.

Declaring Functions #

First thing you do when you write GO code is to declare the main function.

We declare functions using the func keyword followed by the name of the function ( main in this case).

A custom hello world function would look something like this.

Function Arguments #

Let's add an argument to our SayHello function.

Just like that you can keep adding as many arguments as required.

If there are two arguments of the same type declared back to back, you can omit the type declaration of the arguments except the last one, so here firstName and lastName are declared back to back and have the same type string , we can omit the type for firstName .

Variadic Functions #

Go allows you to create functions where you can pass any number of arguments when calling the function. Let's declare a function that will take any number of string s and print them separately on each line.

You can make an argument a variadic argument using the ... syntax, here ...string will accept any number of string s when PrintLines is being called.

An important thing to note here is that inside PrintLines function the type of argument lines is []string , so it is a slice of strings. Whenever you use variadic arguments it will be a slice of a type.

⚠ Note : Variadic argument can only be the final argument of the function, once you have a variadic argument declared you cannot declare anything else after it, so the below code will not compile.

Function Returns #

Let's take our SayHello function, but this time rather than printing lets return the string.

Multiple Return Values #

In golang you can return as many values as you want, lets change the SayHello function to return the line as well as its length.

Ignoring values in multiple return #

When a function returns multiple values, you have to capture all of the variables, you don't get a choice to store just one value in a variable.

To solve this problem go provides a way to ignore a value by using _ . Whatever value you want to ignore, rather than storing it in a variable, use _ .

Basically, you are telling go, "Hey GO! I acknowledge that this function returns two variables, but I don't care about the second one" . Some people find this annoying, but trust me this is a very powerful concept which makes you think about everything that the function returns.

The error Pattern #

I will cover error handling in golang in another article but it is worth touching this topic briefly because it shows up everywhere, in golang there is no try/catch , the way we handle errors is by returning them from functions. Let's see an example.

Read the above example 3 times, understand it properly because if you plan to use go for serious development this pattern of error handling is everywhere, literally everywhere.

It is nothing compliated, a function returns an error type, you store the error in a variable, if the error is not nil there is an error, else you proceed with normal execution 🚗.

Named returns #

Go allows you to pre-declare return variables when declaring the return types of a function, let's see how this works.

Look at the return types of SayHello function, not only do we specify the type but also the name, what GO does is it makes the line and length variable available inside the function body as variables , you can change the value of these variables inside the function body. When writing the return statement, you can just use the return keyword and go will automatically return these variables, this is called naked return .

⚠️ While this feature of GO might look appealing and it has its benefits, please try to avoid using it, using named return can make your code hard to read and understand. Even the official "A Tour of Go" says it:

Naked return statements should be used only in short functions, as with the example shown here. They can harm readability in longer functions.

Be a good gopher .

The defer Keyword #

When calling a function (B) from within a function (A), GO allows you to defer the execution of the function (B) until the calling function (A) finishes its execution. This can be achieved using the defer keyword.

In the above example SayHelloA calls the SayHelloB function using the defer keyword, what this will do is defer the execution of SayHelloB until the complete body of SayHelloA is executed, so it will first print Hello A and then it prints Hello B . If you remove the defer keyword SayHelloB is executed first and then the print statement in SayHelloA is executed.

Notice closely that it seems like you are calling SayHelloB function because there are () after the function, but that is not the case, when using defer keyword you have to use the braces () , but the function is not called immediately it will be deferred.

Here is another example where we are calculating the execution time of a function.

In the above example we are using the time package to store the start and end time of the function, we could have calculated the execution time by just placing the end time calulcate statement after the for loop, but what this pattern allows us to do is create a general function that we can use everywhere, let's see how.

In case you have multiple defer s in a function, the execution order is last in first out, so the last defer will be executed first.

Deferring a function execution is very helpful functionality and you will be using it often when writing software using GO.

This article has been on the lengthier side but now you have the ability to write effective functions in GO 🔨. There is much more to functions that we haven't covered in this article (such as methods), I will cover those topics in another article so keep an eye 👀 on the blog for updates.

Get notified once/twice per month when new articles are published.

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Home » Golang » Golang Find Output Programs

Golang Basics | Find Output Programs | Set 1

This section contains the Golang basics find output programs (set 1) with their output and explanations. Submitted by Nidhi , on August 06, 2021

Explanation:

In the above program, we used fmt.Print() , fmt.Println() , and fmt.Printf() functions to print the value of var1 variable.

There is no such printf() function in fmt package, the correct function is Printf() .

The above program will generate a syntax error because we created the variable var1 but it was not used.

While declaring the variable var1 , we used data type " Int " which is not defined in Golang. The correct data type for integer is " int ".

The above program will generate a syntax error, because the function fmt.Printf() returns two values but we used only one value as an lvalue.

Golang Find Output Programs »

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• fmt.Fscan() Function in Golang With Examples
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• fmt.Sprintf() Function in Golang With Examples
• fmt.Sprint() Function in Golang With Examples
• fmt.Printf() Function in Golang With Examples
• fmt.print() Function in Golang With Examples
• fmt.Fprintln() Function in Golang With Examples
• fmt.Fprintf() Function in Golang With Examples
• fmt.Errorf() Function in Golang With Examples
• fmt.Scan() Function in Golang With Examples
• fmt.Scanf() Function in Golang With Examples
• fmt.Scanln() Function in Golang With Examples
• fmt.Sscanf() Function in Golang With Examples
• fmt.Fscanf() Function in Golang With Examples
• Compare Println vs Printf in Golang with Examples

fmt.Println() Function in Golang With Examples

In Go language, fmt package implements formatted I/O with functions analogous to C’s printf() and scanf() function. The fmt.Println() function in Go language formats using the default formats for its operands and writes to standard output. Here spaces are always added between operands and a newline is appended at the end. Moreover, this function is defined under the fmt package. Here, you need to import the “fmt” package in order to use these functions.

Here, “a …interface{}” contains some strings including specified constant variables.

Return Value: It returns the number of bytes written and any write error encountered.

In the above code, it can be seen that the function Println() is not containing any space within the specified strings still in output is print space that can be seen from the above output.

In the above code, it can be seen that the function Println() is not using any newline (\n) still in the output it prints new line that can be seen from above shown output.

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Golangで未使用の変数エラーを消す方法

stringconv.Atoi などのerrを二つ目の返り値として返してくれる関数を利用する際、errに代入した後使用しないと実行時にエラーが発生します。

しかしだからといって二つの返り値を変数に格納しないと、割り当てが間違っているという別のエラーが返却されることになります。

そのため必ず返り値を変数に代入する必要があるのですが、未使用エラーを発生させない必要があります。

このような状況の場合、 _ (アンダースコア)を利用するとエラーが発生しなくなります。

これはGo公式では Blank identifier という名称になっているようです。

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assignment mismatch: xlsx.GetRows #75

fboundp commented May 4, 2019

shenwei356 commented May 5, 2019

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