Data in Memory

Data in Memory

BasicTopic6 lessons~5h

Lessons, in order

01 Arrays and SlicesAn array is a fixed-size block of elements, laid out one after another; its length is part of its type and assigning it copies every element. A slice is a three-word header — pointer, … Beginner 55 min 02 Strings, Bytes and RunesA Go string is a two-word header — pointer and length — over a run of bytes that never change. It is not an array of characters. By convention those bytes are UTF-8, in which one character … Beginner 45 min 03 MapsA map is a hash table: it hashes the key to a number, uses that number to pick a place in an array, and stores the key and value there. A map value in Go is a single pointer to a runtime … Intermediate 50 min 04 Pointers and Struct LayoutA pointer is the memory address of a variable: eight bytes that say where something lives. Go pointers are safe — no arithmetic, never dangling, checked for nil — but they still decide what … Intermediate 50 min 05 Interfaces Under the HoodAn interface value is two words: one identifies the concrete type stored inside (and, for interfaces with methods, a table of that type's methods), the other is a pointer to the data. … Intermediate 50 min 06 Generics and IteratorsGenerics let a function or type take a type parameter: func MaxT cmp.Ordered T works for every ordered type, checked at compile time, with no any and no type assertions. A constraint — an … Intermediate 50 min

About this topic

Topic I said slices, strings, maps and interfaces are “small headers that point elsewhere”. This topic draws each header, byte by byte, and shows what follows from the drawing.

#	Lesson	The question it answers
01	Arrays and Slices	What is a slice, and when do two slices share memory?
02	Strings, Bytes and Runes	What is a string made of, and what does converting it cost?
03	Maps	How does a map find a key, and what does it cost in memory?
04	Pointers and Struct Layout	How are fields arranged, and why does field order change a struct’s size?
05	Interfaces Under the Hood	What is inside an interface value, and when is nil not nil?
06	Generics and Iterators	How do type parameters work, and what do they cost?

When you finish you can draw any Go value as boxes and arrows, say how many bytes it occupies, and predict whether an operation copies, shares or allocates.