337go-00sxgo-00sx.xmlGolang › Difference between maps and slicesWithin the go runtime, a map is implemented as a pointer to a struct, so passing a map to a function means that you are copying a pointer. Thus changes made to a map within the functions are reflected in the original.**NOTE**: maps for input parameters or return values should be carefully considered. On an API design level, they are a bad choice because they say nothing about the values contained within. In general one should prefer a struct for these cases.A slice is more complicated. Any modification to a slices contents within a function is reflected in the original, but using append to change the length of the array is not, even if the slice has a capacity greater than its length. This is due to slice being implemented a struct with three fields:int for length int for capcity a pointer to a block of memoryContext338go-00rsgo-00rs.xmlGolangLanguage262go-00rvgo-00rv.xmlInitialize moduleWithin a new directory, initialize a module withThis will create a new file `go.mod`263go-00rxgo-00rx.xmlTypes Zero: Predeclared Default value assigned to declared but unassigned variables Literals: Predeclared Explicitly specified values Integer: Literals Base 10 by default Floating-point: Literals Uses decimal point for fractions Rune: Literals Single character representation String: Literals Two creation methods Booleans: Predeclared Binary true/false values byte: Integer Alias for uint8 int: Integer Signed integer sized to architecture's word size uint: Integer Unsigned integer sized to architecture's word size rune: Integer Alias for int32 uintptr: Integer Integer type for storing pointer values String: Predeclared Immutable sequence of bytes, zero value is empty string 264go-00rygo-00ry.xmlType conversionGo does not support automatic type conversion. All variable types need to be converted to interact.265go-00rzgo-00rz.xmlQuotesDifferent qoutes are used for different contexts.The double qoute " will be used to create string literals, while the backtick is used to create raw string literals. The single qoute ' is used to create runes, a single unicode point. E.g. r := '學'.266go-00s0go-00s0.xmlSlicesSlices will have a zero value of nil and is only comprable with nil and ==. Modifying shared slices will affect all references. Length can differ from capacity267go-00s3go-00s3.xmlCreation268go-00s4go-00s4.xmlModification269go-00s5go-00s5.xmlSlicing270go-00s6go-00s6.xmlCopying271go-00s7go-00s7.xmlArray Conversion272go-00s9go-00s9.xmlWhen to Use What1. `var` declaration (nil slice): When size unknown, no initial data 2. Slice literal: When starting values are known 3. `make`: - With length: For buffers or exact size known - Zero length + capacity: For growing slices273go-00sago-00sa.xmlMemory Management- Capacity doubles when < 256 - Growth slows to ~25/for larger slices - Use full slice expression `s[low:high:max]` to prevent capacity issues - Be careful with shared memory when slicing274go-00sbgo-00sb.xmlStandard Library- `slices.Equal(a, b)`: Compare if length and elements match - `slices.EqualFunc(a, b, fn)`: Custom comparison function275go-00scgo-00sc.xmlMapsMaps are declared as `map[keyType]valueType`. A `nil` map (e.g., `var m map[string]int`) cannot be written to. Use `make` or a map literal for writable maps.276go-00sdgo-00sd.xmlStructsStructs are user-defined types with fields. Define them with `type` and access fields using dot notation.Anonymous structs are inline struct definitions:277go-00sego-00se.xmlPointersUse `&` to get a pointer and `*` to dereference. `nil` pointers cannot be dereferenced.278go-00sfgo-00sf.xmlShadowingInner-scope variables can shadow outer-scope ones: 5 { x := 5 fmt.Println(x) // 5 } fmt.Println(x) // 10]]>279go-00sggo-00sg.xmlControl Flow280go-00shgo-00sh.xmlIfGo's `if` statements do not require parentheses. You can declare variables scoped to the condition: 5 { fmt.Println("Big:", n) } else { fmt.Println("Small:", n) }]]>281go-00sigo-00si.xmlForLoops in go support complete (C-style), condition only, for-range styles.If you don't need the key/index in, the underscore _ can be used, telling go to ignore the value.If you just need the key/index, you can leave off the second variable:282go-00sjgo-00sj.xmlSwitch283go-00skgo-00sk.xmlFunctions284go-00slgo-00sl.xmlVariadic ParametersVariadic functions accept a variable number of arguments as a slice:285go-00smgo-00sm.xmlMultiple Return ValuesFunctions can return multiple values, often used with errors:286go-00sngo-00sn.xmlNamed return valuesFunctions can have names specified for the return values, which predeclares variables that are used within the function to hold the return values. These values are initialized to their zero values allowing you to return them before any explicit use or assignment.287go-00spgo-00sp.xmlClosuresThese are functions defined _within_ a function, and are able to access and modify variables declared in the outer function. Closures allow you to pass fome function state to another function. These can also be returned from a function.Anonymous function `f` can read and write `a` even though `a` is not passed in to the function. Using `:=` instead of `=` inside the closure creates a new `a` that ceases to exist when the closure exits.288go-00sqgo-00sq.xmlWhy use closures?Limit function scope If a function is going to be called from only one other function, but it's called multiple times, you can use an inner function to "hide" the called function. This reduces the number of declarations at a package level, making it easier to find an unused name. Removing logic repetetion Given a piece of logic that is repeated multiple times within a function, a closure can be used to remove that repetition. Passing to funcs/returning from funcs These become really interesting, allowing you to take variables within your function and use those variables outside of the function289go-00svgo-00sv.xmlPointersStandard address (`&`) and indirection/dereferencing (`*`) operators. Pointer tricks such as _pointer arithmetic_ that you can do in C are not allowed in go.Before dereferencing a pointer, you must make sure it is non-nil, otherwise the program will panic if you attempt to dereference a `nil` pointer:The pointer type can be based on any type, and the built in function `new` creates a pointer variable which returns a pointer to a zero-value instance of the type.However, the `new` function is rarely used.For structs use `&` before a struct literal to create a pointer instance. When you need a pointer to a primitive type, declare a variable and then point to it.290go-00swgo-00sw.xmlPointers of constants / literalsConstant literals cannot use `&` because they don't have a memory address, e.g.There are two ways around the problem. The first is to introduce a variable to hold the constant. The second is to write a generic helper function that takes a parameter of any type and returns a pointer to that type:which allows one to write the previous code as**NOTE**: The only time you should use pointer parameters to modify a variable is when the function expects an interface, e.g. JSON.291go-00sxgo-00sx.xmlDifference between maps and slicesWithin the go runtime, a map is implemented as a pointer to a struct, so passing a map to a function means that you are copying a pointer. Thus changes made to a map within the functions are reflected in the original.**NOTE**: maps for input parameters or return values should be carefully considered. On an API design level, they are a bad choice because they say nothing about the values contained within. In general one should prefer a struct for these cases.A slice is more complicated. Any modification to a slices contents within a function is reflected in the original, but using append to change the length of the array is not, even if the slice has a capacity greater than its length. This is due to slice being implemented a struct with three fields:int for length int for capcity a pointer to a block of memory