This is a question about Type "Engine" and "RouterGroup" provided by go language gin

Question

r := gin.Default() 

Default() function returns *Engine. but r calls a function on RouterGroup.

ex)

    r.GET("/api/healthcheck", func(c *gin.Context) {
        c.JSON(200, gin.H{
            "message": "hi",
        })
    })

Definition

// Engine is the framework's instance, it contains the muxer, middleware and configuration settings.
// Create an instance of Engine, by using New() or Default()
type Engine struct {
    RouterGroup

// RouterGroup is used internally to configure router, a RouterGroup is associated with
// a prefix and an array of handlers (middleware).
type RouterGroup struct {
    Handlers HandlersChain
    basePath string
    engine   *Engine
    root     bool
}

Can you explain how this works? what syntax is it

Answer 1

A field without an explicit name is called an "embedded field". The fields and methods of an embedded field's type are "promoted" to the embedding (or "parent") struct. The "promoted" fields and methods of an embedded field's type are directly accessible to the embedding (or "parent") struct. Note that "directly accessible" does not mean "inheritance", it just means that you don't have to specify the embedded field's name in the selector expression. So, r.RouterGroup.GET and r.GET are identical.

https://go.dev/ref/spec#Struct_types