Go modules overview - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Go module initialization command?

You run the command go mod init example.com/mymodule in an empty directory. What will be the content of the go.mod file?

A

module mymodule

go 1.20

B

module example.com/mymodule

go 1.20

C

module example.com/mymodule

require go 1.20

D

module example.com/mymodule

version 1.20

💡 Hint

The go mod init command creates a go.mod file with the module path and Go version.

The go.mod file starts with the module path you specify and the Go language version. The correct format is module example.com/mymodule followed by go 1.20 (or your Go version).

❓ Predict Output

intermediate

What is the output of this Go command to add a dependency?

You run go get github.com/some/dependency@v1.2.3 in a module-enabled project. What happens to the go.mod and go.sum files?

A The <code>go.mod</code> file adds a require line for the dependency and <code>go.sum</code> records checksums.

B Nothing changes until you run <code>go mod tidy</code>.

C The <code>go.mod</code> file adds a replace directive for the dependency version.

D The <code>go.mod</code> file is deleted and <code>go.sum</code> is unchanged.

💡 Hint

Think about what go get does in module mode.

go get adds the dependency to go.mod with a require statement and updates go.sum with cryptographic hashes to verify module integrity.

🔧 Debug

advanced

Why does this Go build fail with a module error?

You have a go.mod file with module example.com/mymodule. Your code imports example.com/othermodule/pkg but you get an error: cannot find module providing package example.com/othermodule/pkg. What is the cause?

A The Go version in <code>go.mod</code> is too old to support modules.

B The import path is invalid because it uses dots instead of slashes.

C The module <code>example.com/othermodule</code> is not required in <code>go.mod</code> and not downloaded.

D The <code>go.sum</code> file is missing.

💡 Hint

Check if the dependency is declared in your module file.

Go modules require that all external packages be listed in go.mod under require. If you import a package not declared or downloaded, Go cannot find it.

📝 Syntax

advanced

Which go.mod snippet correctly specifies a replace directive?

You want to replace the module example.com/old version v1.0.0 with a local path ../local/old. Which snippet is correct?

A dlo/lacol/.. >= 0.0.1v dlo/moc.elpmaxe ecalper

B replace example.com/old v1.0.0 => example.com/local/old

C replace example.com/old v1.0.0 => ../local/old v1.0.0

D replace example.com/old v1.0.0 => ../local/old

💡 Hint

The replace directive uses the syntax: replace [old module] [old version] => [new module or path]

The correct syntax for replace is: replace example.com/old v1.0.0 => ../local/old No version is needed for the local path.

🚀 Application

expert

How many modules are downloaded after running go mod tidy on this project?

Given a go.mod file requiring github.com/pkg/errors v0.9.1 and golang.org/x/net v0.0.0-20210428140749-89ef3d95e781, and your code imports only github.com/pkg/errors, what will go mod tidy do?

A It will remove <code>golang.org/x/net</code> from <code>go.mod</code> and download only <code>github.com/pkg/errors</code>.

B It will keep both modules in <code>go.mod</code> and download both.

C It will remove both modules from <code>go.mod</code> because they are not used directly.

D It will add new modules for transitive dependencies but keep both original modules.

💡 Hint

go mod tidy cleans unused dependencies from go.mod.

go mod tidy removes dependencies not used in the code. Since golang.org/x/net is not imported, it will be removed from go.mod and not downloaded.