Can anyone explain to me what is this line doing? I've never seen this before, I guess.
np.Point, np.Valid = Point{}, false
As stated in this github code
This is not a three comma syntax. It is actually initializing two variables together in a line
np.Point, np.Valid = Point{}, false
is similar to
np.Point = Point{}
np.Valid = false
The Go Programming Language Specification
A tuple assignment assigns the individual elements of a multi-valued operation to a list of variables. There are two forms. In the first, the right hand operand is a single multi-valued expression such as a function call, a channel or map operation, or a type assertion. The number of operands on the left hand side must match the number of values. For instance, if f is a function returning two values,
x, y = f()assigns the first value to x and the second to y. In the second form, the number of operands on the left must equal the number of expressions on the right, each of which must be single-valued, and the nth expression on the right is assigned to the nth operand on the left:
one, two, three = '一', '二', '三'
A tuple assignment assigns the individual elements of a multi-valued operation to a list of variables. In the second form, the number of operands on the left must equal the number of > expressions on the right, each of which must be single-valued, and the nth expression on the right is assigned to the nth operand on the left.
In your example,
np.Point, np.Valid = Point{}, false
Or, equivalently,
t1 := Point{}
t2 := false
np.Point = t1
np.Valid = t2