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Some Simple Summaries

Index

Types whose values may have indirect underlying parts.
Types which values can be used as arguments of built-in len function (and cap, close, delete, make functions).
Comparison of built-in container types.
Types which values can be represented with composite literals (T{...}).
Value sizes of all kinds of types.
Types which zero values can be represented with nil.
Types we can implement methods for.
Types which can be embedded in struct types.
Functions whose calls will/may be evaluated at compile time.
Values that can't be taken addresses.
Types which don't support comparisons.
Which code elements are allowed to be declared but not used.
Named source code elements which can be declared together within ().
Named source code elements which can be declared both inside functions and outside any functions.
Expressions which evaluation results may contain optional additional values.
Ways to block the current goroutine ‎forever by using the channel mechanism.
Ways to concatenate strings.
Optimizations made by the standard Go compiler.
Run-time panic and crash cases.

Types whose values may have indirect underlying parts

Types whose values may have indirect underlying parts:

string types
function types
slice types
map types
channel types
interface types

The answer is based on the implementation of the standard Go compiler/runtime. In fact, whether or not function values may have indirect underlying parts is hardly to prove, and string values and interface values should be viewed as values without indirect underlying parts in logic. Please read value parts for details.

Types which values can be used as arguments of built-in `len` function (and `cap`, `close`, `delete`, `make` functions)

	len	cap	close	delete	make
string	Yes
array (and array pointer)	Yes	Yes
slice	Yes	Yes			Yes
map	Yes			Yes	Yes
channel	Yes	Yes	Yes		Yes

Values of above types can also be ranged over in for-range loops.

Types which values can be used as arguments of built-in function len can be called container types in broad sense.

Comparison of built-in container types

Type	Can New Elements Be Added into Values?	Are Elements of Values Replaceable?	Are Elements of Values Addressable?	Will Element Accesses Modify Value Lengths?	May Values Have Underlying Parts
string	No	No	No	No	Yes⁽¹⁾
array	No	Yes⁽²⁾	Yes⁽²⁾	No	No
slice	No⁽³⁾	Yes	Yes	No	Yes
map	Yes	Yes	No	No	Yes
channel	Yes⁽⁴⁾	No	No	Yes	Yes

⁽¹⁾ For the standard Go compiler/runtime.
⁽²⁾ For addressable array values only.
⁽³⁾ Generally, a slice value are modified by assigned another slice value to it by overwriting it. Here, such cases are not viewed as "add new elements". In fact, slice lengths can also be modified separately by calling the reflect.SetLen function. Increase the length of a slice by this way is kind of adding new elements into the slice. But the reflect.SetLen function is slow, so it is rarely used.
⁽⁴⁾ For buffered channels which are still not full.

Types which values can be represented with composite literals (`T{...}`)

Values of the following four kinds of types can be represented with composite literals:

Type (`T`)	Is `T{}` a Zero Value of `T`?
struct	Yes
array	Yes
slice	No (zero value is `nil`)
map	No (zero value is `nil`)

Value sizes of all kinds of types

Please read value copy cost for details.

Types which zero values can be represented with `nil`

The zero values of the following types can be represented with nil.

Type (`T`)	Size of `T(nil)`
pointer	1 word
slice	3 words
map	1 word
channel	1 word
function	1 word
interface	2 words

The above listed sizes are for the standard Go compiler. One word means 4 bytes on 32-bit architectures and 8 bytes on 64-bit architectures. and the indirect underlying parts of a value don't contribute to the size of the value.

The size of a zero value of a type is the same as any other values of the same type.

Types we can implement methods for

Please read methods in Go for details.

Types which can be embedded in struct types

Please read which types can be embedded for details.

Functions whose calls will/may be evaluated at compile time

If a function call is evaluated at compile time, its return results must be constants.

Function	Return Type	Are Calls Always Evaluated at Compile Time?
unsafe.Sizeof	`uintptr`	Yes, always. But please note that the result of such a call is not viewed as a constant if the argument type of the call is a type parameter.
unsafe.Alignof
unsafe.Offsetof
len	`int`	Not always. From Go specification: 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. Please note that, even if such a function call is evaluated at compile-time, the evaluation result is not viewed as a constant if the argument type of the call is a type parameter.
cap	`int`
real	The result is an untyped value. Its default type is `float64`.	Not always. From Go spec: the expressions `real(s)` and `imag(s)` are constants if `s` is a complex constant.
imag
complex	The result is an untyped value. Its default type is `complex128`.	Not always. From Go spec: the expression `complex(sr, si)` is constant if both `sr` and `si` are numeric constants.

Addressable and unaddressable values

Please read this FAQ item to get which values are addressable or unaddressable.

Types which don't support comparisons

Please read this FAQ item to get which values are addressable or unaddressable.

Which code elements are allowed to be declared but not used

	Allowed to Be Declared but Not Used?
import	No
type	Yes
variable	Yes for package-level variables. No for local variables (for the standard compiler).
constant	Yes
function	Yes
label	No

Named source code elements which can be declared together within `()`

Following source code elements (of the same kind) can be declared together within ():

import
type
variable
constant

Functions can't be declared together within (). Also labels.

Named source code elements which can be declared both inside functions and outside any functions

Following named source code elements can be declared both inside functions and outside any functions:

type
variable
constant

Imports must be declared before declarations of other elements (and after the package clause).

Functions can only be declared outside any functions. Anonymous functions can be defined inside other function bodies, but such definitions are not function declarations.

Labels must be declared inside functions.

Expressions which evaluation results may contain optional additional values

The evaluation results of the following expressions may contain optional additional values:

	Syntax	Meaning of The Optional Value (`ok` in the syntax examples)	Will Omitting the Optional Result Affect Program Behavior?
map element access	`e, ok = aMap[key]`	whether or not the accessed key is present in the map	No
channel value receive	`e, ok = <- aChannel`	whether or not the received value was sent before the channel was closed	No
type assertion	`v, ok = anInterface.(T)`	whether or not the dynamic type of the interface value matches the asserted type	Yes (when the optional bool result is omitted, a panic occurs if the assertion fails.)

Ways to block the current goroutine ‎forever by using the channel mechanism

Without importing any package, we can use the following ways to make the current goroutine ‎enter (and stay in) blocking state forever:

send a value to a channel which no ones will receive values from

make(chan struct{}) <- struct{}{}
// or
make(chan<- struct{}) <- struct{}{}

receive a value from a never-closed channel which no values have been and will be sent to

<-make(chan struct{})
// or
<-make(<-chan struct{})
// or
for range make(<-chan struct{}) {}

receive a value from (or send a value to) a nil channel

chan struct{}(nil) <- struct{}{}
// or
<-chan struct{}(nil)
// or
for range chan struct{}(nil) {}

use a bare select block
```
select{}
```

Ways to concatenate strings

Please read strings in Go for details.

Optimizations made by the standard Go compiler

Please read the Go 101 wiki article for this summary.

Run-time panic and crash cases

Please read the Go 101 wiki article for this summary.

Index↡

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Index:

About Go 101 - why this book is written.
Acknowledgments

An Introduction of Go - why Go is worth learning.
The Go Toolchain - how to compile and run Go programs.

Become Familiar With Go Code
- Introduction of Source Code Elements
- Keywords and Identifiers
- Basic Types and Their Value Literals
- Constants and Variables - also introduces untyped values and type deductions.
- Common Operators - also introduces more type deduction rules.
- Function Declarations and Calls
- Code Packages and Package Imports
- Expressions, Statements and Simple Statements
- Basic Control Flows
- Goroutines, Deferred Function Calls and Panic/Recover

Go Type System
- Go Type System Overview - a must read to master Go programming.
- Pointers
- Structs
- Value Parts - to gain a deeper understanding into Go values.
- Arrays, Slices and Maps - first-class citizen container types.
- Strings
- Functions - function types and values, including variadic functions.
- Channels - the Go way to do concurrency synchronizations.
- Methods
- Interfaces - value boxes used to do reflection and polymorphism.
- Type Embedding - type extension in the Go way.
- Type-Unsafe Pointers
- Generics - use and read composite types
- Reflections - the reflect standard package.