mixture of field:value and value initializers

A brief explanation.

The reason you get that is because you are allowed to only use one of the two types of initializers and not both.

i.e. you can either use field:value or value.

Using your example you either do

field:value

t := T2{
    T2_Text: "Test",
    T1: T1{T1_Text: "Test"},
}

or only values

t := T2{
    "Test",
    T1{"Test"},
}

Hope that explains the why

Missing the attribute name T1 for assignment.

t := T2{
    T2_Text: "Test",
    T1:      T1{T1_Text: "Test"},
}

P.S. Just moved @twotwotwo's comment to an answer.

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