3 min read
Allocation
Today’s topic: Allocation! What? You thought allocation was relegated to languages like C and C++? Yeah, that’s actually pretty close to true. We’re not learning about malloc today. Rather, we’re learning about the built-in function new, which gives us just one (of many!) ways to allocate memory for a variable. Allocation The built-in function new takes a type T, allocates storage for a variable of that type at run time, and returns a value of type *T pointing to it.
3 min read
Min and max
I always try to add my own commentary, examples, or other explanation in these emails. Today I’m not really sure what to add. min and max are such basic, and self-evident features, that the biggest surprise about these is that they’re such recent additions to the language. They were added just barely a year ago, with Go 1.21. I will add a bit after we read about min and max, though.
3 min read
Making slices, maps and channels
Making slices, maps and channels The built-in function make takes a type T, optionally followed by a type-specific list of expressions. The core type of T must be a slice, map or channel. It returns a value of type T (not *T). The memory is initialized as described in the section on initial values. Call Core type Result make(T, n) slice slice of type T with length n and capacity n make(T, n, m) slice slice of type T with length n and capacity m make(T) map map of type T make(T, n) map map of type T with initial space for approximately n elements make(T) channel unbuffered channel of type T make(T, n) channel buffered channel of type T, buffer size n The only time you absolutely need to use make is when creating channels.
2 min read
Constant lengths and expressions
A few of the built-in functions are very special, in that they can evaluate to constant expressions. len and cap are two such functions. But they aren’t always evaluated to constant expressions, sometimes they’re more normal-ish runtime functions. Length and capacity … The expression len(s) is constant if s is a string constant. The expressions len(s) and cap(s) are constants if the type of s is an array or pointer to an array and the expression s does not contain channel receives or (non-constant) function calls; in this case s is not evaluated.
2 min read
Capacity of slices
Length and capacity … The capacity of a slice is the number of elements for which there is space allocated in the underlying array. At any time the following relationship holds: 0 <= len(s) <= cap(s) Recall that a slice is backed by a fixed-length array, which may have more elements than the slice. When this is the case, the capacity of the slice is said to be the current length of the slice, plus any unused elements in the backing array that extend beyond the final element of the slice.
2 min read
Length and capacity
Length and capacity The built-in functions len and cap take arguments of various types and return a result of type int. The implementation guarantees that the result always fits into an int. Recall that int is either a 32- or 64-bit integer. So this means that the theoretical maximum length or capacity of the various types that support len and cap depends on the CPU architecture. However, this should not matter in practice, since you’d quickly exceed the available memory, before you had a slice, array, map, or other item with 2^32 elements in it.
1 min read
Deletion of map elements
Deletion of map elements The built-in function delete removes the element with key k from a map m. The value k must be assignable to the key type of m. delete(m, k) // remove element m[k] from map m We already looked at clear, which deletes everything in a map. delete lets you surgically remove individual keys from a map. Unlike some languages, which give you the means to return an element as it’s deleted, if you want to do that in Go, you’ll need to do it in two steps:
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3 min read
Manipulating complex numbers
Today we’re looking at what are almost certainly the least used built-in functions in Go. This is why I’m covering it all in a single day, even though there’s enough material here to potentially justify two or three. Manipulating complex numbers Three functions assemble and disassemble complex numbers. The built-in function complex constructs a complex value from a floating-point real and imaginary part, while real and imag extract the real and imaginary parts of a complex value.
2 min read
Close
Today we’re looking at the close built-in function. There’s not really any new information here, as we’ve already talked about channels, but it’s a good opportunity to review. Close For an argument ch with a core type that is a channel, the built-in function close records that no more values will be sent on the channel. It is an error if ch is a receive-only channel. Sending to or closing a closed channel causes a run-time panic.
2 min read
Clear
Clear The built-in function clear takes an argument of map, slice, or type parameter type, and deletes or zeroes out all elements [[Go 1.21(https://go.dev/ref/spec#Go_1.21)]]. Call Argument type Result clear(m) map[K]T deletes all entries, resulting in an empty map (len(m) == 0) clear(s) []T sets all elements up to the length of s to the zero value of T clear(t) type parameter see below clear is a relatively recent addition to Go, added just over a year ago.
3 min read
Copying slices
Appending to and copying slices … The function copy copies slice elements from a source src to a destination dst and returns the number of elements copied. The core types of both arguments must be slices with identical element type. The number of elements copied is the minimum of len(src) and len(dst). As a special case, if the destination’s core type is []byte, copy also accepts a source argument with core type bytestring.