There are two major things coming in Go 1.18 that you need to know: Type Parameters (generics) and Fuzz Testing, but why are they so important?

The Golang team is hard at work on Golang , which will be released in February 2022, and it looks like it’s going to be a big one. Golang 1.18 will introduce generics (called type parameters) as well as fuzzy testing, which has the potential to change how we develop and test Golang programs for good! We’ll take a look at both of these new features below.

Type Parameters (aka Parameters)

Type parameters (also known as generics in other languages) will allow Go programmers to define functions and methods with a placeholder type name. This will allow developers to write code that can be reused throughout different parts of the project but still work generically for all the types of data they expect it to support.

Let’s take a look at a normal Go function (before 1.
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18), which returns the lowest number of two inputs:

As you can see, we take two integers as parameters. min(1,2)and min(2,1)will both return 1. So far so good, but what happens when you want to get the lowest number of two float values? We would have to write a new function, which takes two float values as parameters, and we wouldn’t be able to reuse the code from our first one. The body of the function would still be the exact same code. If we want to get the minimum of two float64 values, we would have to introduce the same function again with float64 as parameters.

Now let’s take a look at generics in Go:

The biggest change that generics bring is that you can now define functions with an arbitrary placeholder type name which will later serve as a parameter for other types. In Go, generics are written in the form of type T.

This means that you can define a function with any placeholder type name, which will be filled in later by another parameter. So let’s refactor our previous example to the new generic approach:

As you can see, the code is a bit longer. First, we have an interface, which declares all numeric types into a new type called “numeric.” That means we can use float64and intinside generics. Then we define a new function called minas we did before.

The difference Parameters

That now the function has a type parameter in the head: min[T numeric.  This tells Go that the type Tshould be a numeric type, so anything of the ones we declared in the interface. After that, everything is normal again, and we declare the function as we did before, except that we replace intwith T.

If the new function gets called now, Go will check if the type provided by the user fits into the interface. If so, it will replace Twith that type in the whole function. So if we input a number of type int, we will also get an integer back. If we input a float64, we will get a float64returned and so on. So instead of writing 12 functions, with the exact same content, but different parameter types for every numeric type in Go, we now have a single “all-rounder” function.

Parameters Fuzzy Testing

In addition to generics, Go will also have fuzzy testing built-in from the start with Golang version 1.18. Fuzzy testing allows a test to be run against a large number of different inputs. For example, we have a function that takes in two numbers as a parameter and does something with them. We now want to ensure that the function works properly with unit tests.

The normal approach would be to write a test for every number we expect the function to handle. If our input data is [0, 100], [200, 100], and [1234, 4321], then we would have three tests in total. But what if the user inputs something that we didn’t think of? Maybe a negative number? So we would also have to test those. There is a lot more.

The original developer of the function might not think about large numbers, as they think nobody would ever insert a large number into the function, but maybe somebody does. So they would also have to cover those, to not crash the program. With numbers, this might be easy, but what if the test only fails with an input of.

All other numbers work just fine.

A developer can’t test every possible input value. That’s where fuzzy testing comes in. Fuzzy testing inputs a lot of random values into your functions to test them.
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Here is how it’s done:

The test must be in a file as a function. The name FuzzXxxand should take a argument just like a takes. This is the basic syntax of a fuzzing test:

In the second line, you can see that we have a normal test parameter.
The first parameter tis for everything that you would do to a normal unit test. But the later parameters are more interesting. You can actually use any type there, and Go will automatically run the body with random. Inputs for that parameter, which fits your type.

So if our test function takes in a numeric type, Go will run it with random numbers. You can then check the error as you would normally do. You don’t have to worry about the test set. Everything will be handle the fuzzy testing package.


If you are a Golang developer, the upcoming release of Go 1.18 will bring two major changes that may change how you work with generics and fuzzy testing in your code.

With generics, programmers can create functions to handle. Any type without having to write 12 different versions for every numeric type. Fuzzy testing allows developers to run unit tests against random values. Which helps ensure more possible input data is cover in test.