mirror of
https://github.com/go-delve/delve.git
synced 2025-11-01 03:42:59 +08:00
82ece54737
* documentation: copied old documentation from wiki * command: better online documentation Help without arguments prints just a short summary for each command, help followed by a command prints the command's syntax and a longer explanation. * documentation: automatically generate Documentation/cli/README.md
83 lines
2.6 KiB
Markdown
83 lines
2.6 KiB
Markdown
# Expressions
|
|
|
|
Delve can evaluate a subset of go expression language, specifically the following features are supported:
|
|
|
|
- All (binary and unary) on basic types except <-, ++ and --
|
|
- Comparison operators on any type
|
|
- Type casts between numeric types
|
|
- Type casts of integer constants into any pointer type
|
|
- Struct member access (i.e. `somevar.memberfield`)
|
|
- Slicing and indexing operators on arrays, slices and strings
|
|
- Map access
|
|
- Pointer dereference
|
|
- Calls to builtin functions: `cap`, `len`, `complex`, `imag` and `real`
|
|
- Type assertion on interface variables (i.e. `somevar.(concretetype)`)
|
|
|
|
# Nesting limit
|
|
|
|
When delve evaluates a memory address it will automatically return the value of nested struct members, array and slice items and dereference pointers.
|
|
However to limit the size of the output evaluation will be limited to two levels deep. Beyond two levels only the address of the item will be returned, for example:
|
|
|
|
```
|
|
(dlv) print c1
|
|
main.cstruct {
|
|
pb: *struct main.bstruct {
|
|
a: (*main.astruct)(0xc82000a430),
|
|
},
|
|
sa: []*main.astruct len: 3, cap: 3, [
|
|
*(*main.astruct)(0xc82000a440),
|
|
*(*main.astruct)(0xc82000a450),
|
|
*(*main.astruct)(0xc82000a460),
|
|
],
|
|
}
|
|
```
|
|
|
|
To see the contents of the first item of the slice `c1.sa` there are two possibilities:
|
|
|
|
1. Execute `print c1.sa[0]`
|
|
2. Use the address directly, executing: `print *(*main.astruct)(0xc82000a440)`
|
|
|
|
# Elements limit
|
|
|
|
For arrays, slices, strings and maps delve will only return a maximum of 64 elements at a time:
|
|
|
|
```
|
|
(dlv) print ba
|
|
[]int len: 200, cap: 200, [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,...+136 more]
|
|
```
|
|
|
|
To see more values use the slice operator:
|
|
|
|
```
|
|
(dlv) print ba[64:]
|
|
[]int len: 136, cap: 136, [0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,...+72 more]
|
|
```
|
|
|
|
For this purpose delve allows use of the slice operator on maps, `m[64:]` will return the key/value pairs of map `m` that follow the first 64 key/value pairs (note that delve iterates over maps using a fixed ordering).
|
|
|
|
# Interfaces
|
|
|
|
Interfaces will be printed using the following syntax:
|
|
```
|
|
<interface name>(<concrete type>) <value>
|
|
```
|
|
|
|
For example:
|
|
|
|
```
|
|
(dlv) p iface1
|
|
(dlv) p iface1
|
|
interface {}(*struct main.astruct) *{A: 1, B: 2}
|
|
(dlv) p iface2
|
|
interface {}(*struct string) *"test"
|
|
(dlv) p err1
|
|
error(*struct main.astruct) *{A: 1, B: 2}
|
|
```
|
|
|
|
To use a field of a struct contained inside an interface variable use a type assertion:
|
|
|
|
```
|
|
(dlv) p iface1.(*main.astruct).B
|
|
2
|
|
```
|