Go Interview Questions and Answers 2025

The 'defer' statement in Go is used to ensure that a function call is performed later in the program's execution, usually for purposes of cleanup. It is often used to close files or unlock mutexes after they have been opened or locked, respectively. The deferred function will execute after the surrounding function completes, even if it exits due to a panic.

In Go, an array is a fixed-size sequence of elements of the same type, while a slice is a dynamically-sized, flexible view into the elements of an array. Slices are more powerful and commonly used than arrays because they can grow and shrink in size.

A goroutine is a lightweight thread managed by the Go runtime. It allows concurrent execution of functions, enabling developers to write programs that can perform multiple tasks simultaneously without the overhead of traditional threads.

The 'select' statement in Go is used to wait on multiple channel operations. It allows a goroutine to wait for multiple communication operations, making it easier to handle multiple channels and synchronize between them.

A buffered channel in Go has a capacity to hold a certain number of values before blocking the sender, while an unbuffered channel does not have any capacity and requires both the sender and receiver to be ready at the same time for communication to occur.

The 'interface' type in Go is used to define a contract that types can implement. It allows for polymorphism, enabling different types to be treated as the same type if they implement the same methods. This is a key feature of Go's type system.

The 'init' function in Go is a special function that is automatically executed when a package is initialized. It is used to set up any necessary state or perform initialization tasks before the main program starts executing.

The 'panic' function in Go is used to raise a runtime error, causing the program to stop executing. The 'recover' function is used to regain control of a panicking goroutine, allowing the program to continue executing after handling the panic.

The 'go' keyword in Go is used to start a new goroutine, which is a lightweight thread managed by the Go runtime. It allows for concurrent execution of functions, enabling developers to write programs that can perform multiple tasks simultaneously.

The 'package' keyword in Go is used to define a package, which is a collection of related Go source files. It is used to organize code into reusable modules and to manage dependencies between different parts of a program.

The 'import' statement in Go is used to include other packages in a Go program. It allows developers to use functions, types, and variables defined in other packages, enabling code reuse and modular programming.

The 'struct' type in Go is used to define a composite data type that groups together variables (fields) under a single name. It allows developers to create complex data structures that can hold multiple values of different types.

The 'map' type in Go is used to define a collection of key-value pairs. It allows for efficient retrieval of values based on their keys, making it a powerful data structure for storing and accessing data.

The 'go mod' command in Go is used to manage dependencies in Go projects. It allows developers to define and manage module dependencies, ensuring that the correct versions of packages are used in a project.

The 'go run' command in Go is used to compile and run Go programs. It allows developers to quickly test and execute Go code without needing to create a binary executable.

The 'go build' command in Go is used to compile Go source code into a binary executable. It generates an executable file that can be run on the target platform, allowing developers to create standalone applications.

The 'go test' command in Go is used to run tests for Go packages. It automatically discovers and executes test functions, providing a framework for writing and running unit tests in Go programs.

The 'go fmt' command in Go is used to format Go source code according to standard conventions. It automatically adjusts the spacing, indentation, and alignment of code, ensuring a consistent style across Go programs.

The 'go vet' command in Go is used to analyze Go source code and report potential issues or bugs. It performs static analysis on the code, helping developers identify common mistakes and improve code quality.

The 'go doc' command in Go is used to display documentation for Go packages, functions, and types. It provides a way for developers to access and read documentation directly from the command line, making it easier to understand how to use different parts of the Go standard library and third-party packages.

A 'nil' slice in Go has no underlying array and both its length and capacity are zero. An empty slice, on the other hand, has an underlying array with zero elements, but it is not 'nil'. You can check if a slice is 'nil' using 'slice == nil'.

Go uses a garbage collector to automatically manage memory. It identifies and frees memory that is no longer in use, reducing the need for manual memory management. This simplifies development but requires understanding how memory is allocated and released.

The 'context' package in Go is used to manage deadlines, cancellations, and other request-scoped values across API boundaries and goroutines. It is commonly used to control the lifecycle of processes and manage timeouts.

A worker pool in Go can be implemented using goroutines and channels. You create a fixed number of worker goroutines that listen on a shared channel for tasks, process them, and send results back through another channel.

'sync.Mutex' is used to provide mutual exclusion for critical sections, allowing only one goroutine to access the section at a time. 'sync.RWMutex' allows multiple readers or one writer, making it more efficient for read-heavy workloads.

The 'select' statement with a 'default' case allows non-blocking channel operations. If no other case is ready, the 'default' case is executed immediately, enabling the program to continue without waiting.

Errors in Go are handled by returning an 'error' value from functions. The 'errors' package provides functions to create and manipulate error values, including wrapping errors with additional context using 'fmt.Errorf'.

'sync.WaitGroup' is used to wait for a collection of goroutines to finish, while channels are used for communication and synchronization between goroutines. 'WaitGroup' is simpler for waiting, but channels provide more flexibility.

Go implements interfaces using a pair of pointers: one to the type information and another to the actual data. This allows dynamic dispatch of methods and enables polymorphism.

The 'unsafe' package in Go provides low-level operations that violate the type safety of Go programs. It is used for advanced scenarios like memory manipulation but should be used with caution as it can lead to undefined behavior.

Race conditions in Go can be prevented using synchronization primitives like 'sync.Mutex', 'sync.RWMutex', or by using channels to coordinate access to shared resources.

'runtime.GOMAXPROCS' sets the maximum number of OS threads that can execute Go code simultaneously, while 'runtime.NumCPU' returns the number of logical CPUs available on the system.

Custom marshaling and unmarshaling for JSON in Go can be implemented by defining 'MarshalJSON' and 'UnmarshalJSON' methods for a type. These methods allow you to control how the type is serialized and deserialized.

'time.Ticker' is used to send periodic ticks on a channel, while 'time.Timer' is used to send a single event after a specified duration. Both are used for time-based operations but serve different purposes.

Deadlocks in Go can be avoided by carefully designing goroutines and their interactions. Techniques include using proper locking order, avoiding circular dependencies, and using channels to coordinate goroutines.

The 'reflect' package in Go is used for runtime reflection, allowing programs to inspect and manipulate the types and values of variables at runtime. It is useful for writing generic code but can be complex and slower.

A singleton pattern in Go can be implemented using a 'sync.Once' to ensure that the instance is created only once, even in the presence of concurrent goroutines.

'os.Exit' terminates the program immediately with a specified exit code, bypassing deferred function calls. 'return' in the 'main' function allows deferred functions to execute before the program exits.

Build tags in Go are used to include or exclude files from a build based on conditions. They are specified as comments at the top of a file and allow for platform-specific or environment-specific builds.

The 'sync.Cond' type in Go is used to coordinate goroutines by allowing one or more goroutines to wait until a condition is met. It is typically used with 'sync.Mutex' to protect shared state.

The 'context.Context' type in Go is used to carry deadlines, cancellation signals, and request-scoped values across API boundaries and goroutines. It is a key part of managing the lifecycle of requests in concurrent programs.

The 'sync.Pool' type in Go is used to manage a pool of temporary objects that can be reused to reduce memory allocation overhead. It is useful for managing short-lived objects and improving performance in high-throughput applications.

The 'net/http' package in Go provides HTTP client and server implementations. It allows developers to create web servers, make HTTP requests, and handle HTTP responses, making it a key part of building web applications in Go.

The 'encoding/json' package in Go provides functions for encoding and decoding JSON data. It allows developers to easily convert Go data structures to JSON format and vice versa, making it essential for working with APIs and data interchange.

The 'encoding/xml' package in Go provides functions for encoding and decoding XML data. It allows developers to easily convert Go data structures to XML format and vice versa, making it essential for working with XML-based APIs and data interchange.

The 'time' package in Go provides functionality for measuring and displaying time. It includes features for working with durations, timestamps, and time zones, making it essential for handling time-related operations in Go programs.

The 'os' package in Go provides a platform-independent interface to operating system functionality. It includes features for working with files, directories, environment variables, and process management, making it essential for system-level programming in Go.

The 'flag' package in Go provides a way to parse command-line flags and arguments. It allows developers to define flags, set default values, and retrieve the values provided by users when running a Go program, making it essential for building command-line applications.

The 'log' package in Go provides a simple logging interface for writing log messages to standard output or files. It includes features for setting log levels, formatting log messages, and handling log output, making it essential for debugging and monitoring Go applications.

The 'testing' package in Go provides a framework for writing and running tests. It includes features for defining test cases, running benchmarks, and reporting test results, making it essential for ensuring code quality and reliability in Go programs.

The 'time.Time' type in Go represents an instant in time with nanosecond precision. It includes methods for manipulating and formatting time, making it essential for handling date and time operations in Go programs.

The 'time.Duration' type in Go represents a duration of time in nanoseconds. It is used for measuring elapsed time, setting timeouts, and scheduling events, making it essential for time-related operations in Go programs.

The 'sync.WaitGroup' type in Go is used to wait for a collection of goroutines to finish executing. It provides methods to add, wait, and mark completion of goroutines, making it essential for synchronizing concurrent operations.

The 'sync.Mutex' type in Go is used to provide mutual exclusion for critical sections of code. It allows only one goroutine to access a section of code at a time, preventing race conditions and ensuring thread safety.

The 'sync.RWMutex' type in Go is used to provide read-write mutual exclusion for critical sections of code. It allows multiple readers or one writer to access a section of code, making it more efficient for read-heavy workloads.

The 'atomic' package in Go provides low-level atomic memory primitives for synchronizing access to shared variables. It is used to implement lock-free algorithms and ensure safe concurrent access to data.

Custom HTTP middleware in Go can be implemented by creating a function that wraps an 'http.Handler'. The middleware function processes the request and response before or after calling the next handler in the chain.

The 'runtime' package in Go provides functions for interacting with the Go runtime system, such as managing goroutines, garbage collection, and memory statistics. It is useful for low-level performance tuning and debugging.

Memory usage in Go programs can be optimized by reusing objects with 'sync.Pool', avoiding excessive allocations, using slices efficiently, and profiling memory usage with tools like 'pprof'.

The 'build' package in Go provides utilities for inspecting and parsing Go source code and build metadata. It is used for tools that analyze or manipulate Go codebases.

A plugin system in Go can be implemented using the 'plugin' package, which allows loading and symbol resolution of shared object files at runtime. This enables dynamic extension of applications.

The 'cgo' tool in Go is used to enable interoperability with C code. It allows Go programs to call C functions and use C libraries, making it useful for integrating with existing C codebases.

Large file processing in Go can be handled by using streaming techniques, such as reading files in chunks with 'bufio.Reader' or processing data line by line to minimize memory usage.

The 'syscall' package in Go provides low-level access to operating system calls. It is used for advanced system programming but is being replaced by the 'x/sys' package for better portability.

A rate limiter in Go can be implemented using the 'time.Ticker' or 'time.After' functions, or by using the 'golang.org/x/time/rate' package for more advanced rate-limiting algorithms.

The 'pprof' package in Go provides tools for profiling CPU, memory, and goroutine usage. It is used to analyze and optimize the performance of Go programs.

A message queue in Go can be implemented using channels for in-memory queues or by integrating with external systems like RabbitMQ, Kafka, or NATS for distributed messaging.

The 'template' package in Go provides tools for creating and executing text or HTML templates. It is used for generating dynamic content in web applications and other text-based outputs.

A custom logger in Go can be implemented by creating a struct that satisfies the 'io.Writer' interface and adding methods for logging messages with different levels and formats.

The 'net/rpc' package in Go provides support for building RPC (Remote Procedure Call) servers and clients. It allows functions to be called across network boundaries as if they were local.

A circuit breaker in Go can be implemented using state management and timeouts to track failures and prevent further calls to a failing service. Libraries like 'sony/gobreaker' can simplify this process.

The 'net/http/httptest' package in Go provides utilities for testing HTTP servers. It includes tools for creating test servers, recording HTTP responses, and simulating HTTP requests.

A custom error type in Go can be implemented by defining a struct that satisfies the 'error' interface by implementing the 'Error()' method. This allows for more detailed error handling.

The 'golang.org/x/net/context' package in Go provides an earlier implementation of the 'context' package for managing deadlines, cancellations, and request-scoped values. It is now superseded by the standard 'context' package.

A priority queue in Go can be implemented using the 'container/heap' package, which provides tools for managing heap-based data structures.