How do you declare constants in Go?

The answer is: Go applications do not have a mandatory project layout, but the community generally adopts a standard structure to improve maintainability and scalability. 1.cmd/ stores the program entrance, each subdirectory corresponds to an executable file, such as cmd/myapp/main.go; 2.internal/ stores private code, cannot be imported by external modules, and is used to encapsulate business logic and services; 3.pkg/ stores publicly reusable libraries for importing other projects; 4.api/ optionally stores OpenAPI, Protobuf and other API definition files; 5.config/, scripts/, and web/ store configuration files, scripts and web resources respectively; 6. The root directory contains go.mod and go.sum

Using bufio.Scanner is the most common and efficient method in Go to read files line by line, and is suitable for handling scenarios such as large files, log parsing or configuration files. 1. Open the file using os.Open and make sure to close the file via deferfile.Close(). 2. Create a scanner instance through bufio.NewScanner. 3. Call scanner.Scan() in the for loop to read line by line until false is returned to indicate that the end of the file is reached or an error occurs. 4. Use scanner.Text() to get the current line content (excluding newline characters). 5. Check scanner.Err() after the loop is over to catch possible read errors. This method has memory effect

Routing in Go applications depends on project complexity. 1. The standard library net/httpServeMux is suitable for simple applications, without external dependencies and is lightweight, but does not support URL parameters and advanced matching; 2. Third-party routers such as Chi provide middleware, path parameters and nested routing, which is suitable for modular design; 3. Gin has excellent performance, built-in JSON processing and rich functions, which is suitable for APIs and microservices. It should be selected based on whether flexibility, performance or functional integration is required. Small projects use standard libraries, medium and large projects recommend Chi or Gin, and finally achieve smooth expansion from simple to complex.

The if-else statement in Go does not require brackets but must use curly braces. It supports initializing variables in if to limit scope. The conditions can be judged through the elseif chain, which is often used for error checking. The combination of variable declaration and conditions can improve the simplicity and security of the code.

Go's flag package can easily parse command line parameters. 1. Use flag.Type() to define type flags such as strings, integers, and booleans; 2. You can parse flags to variables through flag.TypeVar() to avoid pointer operations; 3. After calling flag.Parse(), use flag.Args() to obtain subsequent positional parameters; 4. Implementing the flag.Value interface can support custom types to meet most simple CLI requirements. Complex scenarios can be replaced by spf13/cobra library.

In Go, constants are declared using the const keyword, and the value cannot be changed, and can be of no type or type; 1. A single constant declaration such as constPi=3.14159; 2. Multiple constant declarations in the block are such as const(Pi=3.14159; Language="Go"; IsCool=true); 3. Explicit type constants such as constSecondsInMinuteint=60; 4. Use iota to generate enumeration values, such as const(Sunday=iota;Monday;Tuesday) will assign values 0, 1, and 2 in sequence, and iota can be used for expressions such as bit operations; constants must determine the value at compile time,

gorun is a command for quickly compiling and executing Go programs. 1. It completes compilation and running in one step, generates temporary executable files and deletes them after the program is finished; 2. It is suitable for independent programs containing main functions, which are easy to develop and test; 3. It supports multi-file operation, and can be executed through gorun*.go or lists all files; 4. It automatically processes dependencies and uses the module system to parse external packages; 5. It is not suitable for libraries or packages, and does not generate persistent binary files. Therefore, it is suitable for rapid testing during scripts, learning and frequent modifications. It is an efficient and concise way of running.

To connect to SQL databases in Go, you need to use the database/sql package and a specific database driver. 1. Import database/sql packages and drivers (such as github.com/go-sql-driver/mysql), note that underscores before the drivers indicate that they are only used for initialization; 2. Use sql.Open("mysql","user:password@tcp(localhost:3306)/dbname") to create a database handle, and call db.Ping() to verify the connection; 3. Use db.Query() to execute query, and db.Exec() to execute