2 min read
Struct field promotion
Yesterday we learned that structs can have embedded fields. Although we didn’t really learn about any of the special powers this gives us. Today we’ll have a look at those powers. One advantage to using an embedded type is that the implicit field name (the one derrived from the type, Person, in our example) can be omitted. This is the result of “promotion”. For example: var e Employee e.Name = "Bob" // equivalent to e.
2 min read
Embedded struct fields
When I introduced structs last week, I skipped over one sentence. Today I’m going to address that. Struct types A struct is a sequence of named elements, called fields, each of which has a name and a type. Field names may be specified explicitly (IdentifierList) or implicitly (EmbeddedField). Within a struct, non-blank field names must be unique. We already saw how field names are expressed explicitly. But what is an embedded field?
3 min read
Blank field names
Yesterday we started talking about Go’s structs, and breezed over a phrase about non-blank field names. Wassat? Struct types … Within a struct, non-blank field names must be unique. Go has a concept of a blank identifier. It looks like the underscore character (_), and is useful in many situations, and we’ll discuss more of them in due time. (It’s also decidedly not useful in some situations where it’s permitted, and I made a video about that a while ago)
2 min read
Struct types
Structs. Now we’re getting to some meaty stuff! Let’s start simple. What is a struct? Struct types A struct is a sequence of named elements, called fields, each of which has a name and a type. … Within a struct, non-blank field names must be unique. Forget about blank field names for now. I’ll talk about that tomorrow. I’m also postponing the EBNF description of structs for a while, because there are actually several subtleties to how structs work in Go, which can get into the weeds very quickly.
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2 min read
Slice dimensions
You may recall from last week’s discussion of N-dimensional arrays that Go doesn’t support multi-dimensional arrays. But the implications of this matter a lot more for slices than they do for arrays. Slice types … Like arrays, slices are always one-dimensional but may be composed to construct higher-dimensional objects. With arrays of arrays, the inner arrays are, by construction, always the same length; however with slices of slices (or arrays of slices), the inner lengths may vary dynamically.
2 min read
Slice capacity
Slice types … The array underlying a slice may extend past the end of the slice. The capacity is a measure of that extent: it is the sum of the length of the slice and the length of the array beyond the slice; a slice of length up to that capacity can be created by slicing a new one from the original slice. The capacity of a slice a can be discovered using the built-in function cap(a).
2 min read
Slice storage
Slice types … The length of a slice s can be discovered by the built-in function len; unlike with arrays it may change during execution. The elements can be addressed by integer indices 0 through len(s)-1. The slice index of a given element may be less than the index of the same element in the underlying array. A slice, once initialized, is always associated with an underlying array that holds its elements.
1 min read
Slice types
So we’ve learned about the fixed-length, and therefore somewaht limited, array types. Let’s now look at the more flexible cousin, the slice. Slice types A slice is a descriptor for a contiguous segment of an underlying array and provides access to a numbered sequence of elements from that array. A slice type denotes the set of all slices of arrays of its element type. The number of elements is called the length of the slice and is never negative.
2 min read
Recursive arrays
Today, our final note on array types, and when recursion of types is, and is not, permitted: Array types … An array type T may not have an element of type T, or of a type containing T as a component, directly or indirectly, if those containing types are only array or struct types. // invalid array types type ( T1 [10]T1 // element type of T1 is T1 T2 [10]struct{ f T2 } // T2 contains T2 as component of a struct T3 [10]T4 // T3 contains T3 as component of a struct in T4 T4 struct{ f T3 } // T4 contains T4 as component of array T3 in a struct ) // valid array types type ( T5 [10]*T5 // T5 contains T5 as component of a pointer T6 [10]func() T6 // T6 contains T6 as component of a function type T7 [10]struct{ f []T7 } // T7 contains T7 as component of a slice in a struct ) I think the explanation and provided examples are pretty clear.
1 min read
N-dimensional arrays
There’s one sentence at the end of the paragraph yesterday about arrays, which I saved for today, as I think it deserves special attention: Array types … Array types are always one-dimensional but may be composed to form multi-dimensional types. [3][5]int [2][2][2]float64 // same as [2]([2]([2]float64)) The two examples provided do not represent a 2- and 3-dimensional array, therefore. Rather, they represent an array of arrays, and an array of arrays of arrays, respectively.
2 min read
Array types
Arrays should not be a foreign concept to anyone who’s done programming before. But Go’s version of arrays has some peculiarities that often trip up beginners. Array types An array is a numbered sequence of elements of a single type, called the element type. The number of elements is called the length of the array and is never negative. ArrayType = "[" ArrayLength "]" ElementType . ArrayLength = Expression . ElementType = Type .