How to properly initialize a golang struct with default values?
Jun 30, 2025 am 01:53 AMIn Go, structure default initialization can be achieved through constructors, nested structures, or reflections. 1. It is recommended to use a constructor starting with New to return a structure pointer with a default value to improve readability and scalability; 2. If multiple structures share fields, they can be extracted into an infrastructure and encapsulated default initialization logic to reduce duplicate code; 3. For complex scenarios, if a large number of field default values ??need to be dynamically processed, a general initialization function can be written in combination with field labels and reflections, but pay attention to performance and readability. The standard library does not directly support this function, and some third-party libraries are optional. The core is to keep the initialization logic unified and clear.
In Go, initializing default values ??for structures is not a feature that is directly supported like some other languages. You need to implement it through constructors, methods, or field assignments. If you want the structure to be instantiated automatically with the default value, you need to manually do some encapsulation.

Use the New function to set the default value
The Go community generally recommends using functions starting with New
as constructors to return structure pointers with default values.

type Config struct { Timeout time.Duration Retries int Debug bool } func NewDefaultConfig() *Config { return &Config{ Timeout: 5 * time.Second, Retries: 3, Debug: false, } }
When calling this, just:
cfg := NewDefaultConfig()
The benefits of this method are:

- Strong readability: at a glance, this is a construction method with default values
- Easy to expand: If you want to add more default configurations in the future, you only need to change this function
- Avoid duplicate code
Embed structure multiplexing default value logic
If you have multiple structures sharing part of the field, consider drawing the shared part into an infrastructure and providing it with a default initialization method.
type Base struct { CreatedAt time.Time UpdatedAt time.Time } func DefaultBase() Base { now := time.Now() return Base{ CreatedAt: now, UpdatedAt: now, } } type User struct { Base Name string Age int } user := User{ Base: DefaultBase(), Name: "Alice", }
This method is suitable for when a "template-style" structure appears in a project, and can effectively reduce duplicate initialization code.
Initialize function using field tags (optional)
For more complex scenarios, such as reading the default value from a configuration file or tag tag, a common initialization function can be implemented with the help of reflection. However, this approach is a little more complicated and can easily affect performance and code readability. It is recommended to use it only when it really requires dynamic processing of a large number of fields.
If you just want to simply support default value analysis like yaml
or json
tags, you can refer to the following ideas:
- Define a structure and add tag default value
- Write a general function to scan all fields
- Use reflection to set fields that are not explicitly assigned to the default value
But note: The standard library does not support directly parsing the default values ??in tags. This part needs to be implemented by yourself or with the help of a third-party library.
Basically that's it. Go does not have a built-in default value mechanism, but similar effects can be simulated well with constructors or nested structures. The key is to keep the initialization logic unified and clear, and avoid scattering codes with default value settings everywhere.
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