How to Initialize Slices of Pointers with Anonymous Structs in Golang?

Initializing Slices of Pointers with Anonymous Structs in Golang

In the code snippet from Chapter 7 of GOPL (Section 7.6), an anonymous struct is used to initialize a slice of pointers:

<code class="go">var tracks = []*Track{
    {"Go", "Delilah", "From the Roots Up", 2012, length("3m38s")},
    {"Go", "Moby", "Moby", 1992, length("3m37s")},
    {"Go Ahead", "Alicia Keys", "As I Am", 2007, length("4m36s")},
    {"Ready 2 Go", "Martin Solveig", "Smash", 2011, length("4m24s")},
}</code>

This may seem confusing as the Track type is already defined, and the syntax {1, 2} appears to be initializing a new, unnamed struct. However, this syntax is a shortcut used to initialize the element of the slice type without explicitly defining the struct.

The "{}" notation is essentially equivalent to:

<code class="go">type Ex struct {
    A, B int
}

a := []Ex{Ex{1, 2}, Ex{3, 4}}</code>

Where the type name (Ex) is omitted. This syntax works even when initializing slices of pointers:

<code class="go">c := []*Ex{&Ex{1, 2}, &Ex{3, 4}}
d := []*Ex{{1, 2}, {3, 4}}
e := []*Ex{{1, 2}, &Ex{3, 4}}</code>

In these cases, the & operator is automatically applied to the anonymous struct to create the pointer.

However, attempting to initialize a slice of pointers with a reference to an anonymous struct (without the & operator) will result in a syntax error:

<code class="go">f := []*Ex{&{1, 2}, &{3, 4}} // Syntax Error!</code>

To initialize a slice of pointers with an anonymous struct, either the anonymous struct must be converted to a pointer, or the pointer can be omitted altogether:

<code class="go">f := []struct{
    A, B int
}{
    {1, 2}, {3, 4}
}
// or with pointers...
g := []*struct{
    A, B int
}{
    {1, 2}, {3, 4}
}</code>

Here, the anonymous struct is embedded within the slice of pointers without the need for a separate type definition. This syntax is commonly used to initialize anonymous structs in maps and other collections in Golang.

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