structslop
Package structslop defines an Analyzer that checks if struct fields can be re-arranged to optimize size.
Installation
With Go modules:
go get github.com/orijtech/structslop/cmd/structslopWithout Go modules:
$ cd $GOPATH/src/github.com/orijtech/structslop
$ git checkout v0.0.6
$ go get
$ install ./cmd/structslopUsage
You can run structslop either on a Go package or Go files, the same way as
other Go tools work.
Example:
$ structslop github.com/orijtech/structslop/testdata/src/structor:
$ structslop ./testdata/src/struct/p.goSample output:
/go/src/github.com/orijtech/structslop/testdata/struct/p.go:30:9: struct has size 24 (size class 32), could be 16 (size class 16), you'll save 50.00% if you rearrange it to:
struct {
y uint64
x uint32
z uint32
}
/go/src/github.com/orijtech/structslop/testdata/struct/p.go:36:9: struct has size 40 (size class 48), could be 24 (size class 32), you'll save 33.33% if you rearrange it to:
struct {
_ [0]func()
i1 int
i2 int
a3 [3]bool
b bool
}
/go/src/github.com/orijtech/structslop/testdata/struct/p.go:59:9: struct has size 40 (size class 48), could be 32 (size class 32), you'll save 33.33% if you rearrange it to:
struct {
y uint64
t *httptest.Server
w uint64
x uint32
z uint32
}
/go/src/github.com/orijtech/structslop/testdata/struct/p.go:67:9: struct has size 40 (size class 48), could be 32 (size class 32), you'll save 33.33% if you rearrange it to:
struct {
y uint64
t *s
w uint64
x uint32
z uint32
}
Example, for the first report above, the output meaning:
- The current struct size is
24, the size that the Go runtime will allocate for that struct is32. - The optimal struct size is
16, the size that the Go runtime will allocate for that struct is16. - The layout of optimal struct.
- The percentage savings with new struct layout.
That said, some structs may have a smaller size, but for efficiency, the Go runtime will allocate them in the same size class, then those structs are not considered sloppy:
type s1 struct {
x uint32
y uint64
z *s
t uint32
}and:
type s2 struct {
y uint64
z *s
x uint32
t uint32
}have the same size class 32, though s2 layout is only 24 byte in size.
However, you can still get this information when you want, using -verbose flag:
$ structslop -verbose ./testdata/src/verbose/p.go
/go/src/github.com/orijtech/structslop/testdata/src/verbose/p.go:17:8: struct has size 0 (size class 0)
/go/src/github.com/orijtech/structslop/testdata/src/verbose/p.go:19:9: struct has size 1 (size class 8)
/go/src/github.com/orijtech/structslop/testdata/src/verbose/p.go:23:9: struct has size 32 (size class 32), could be 24 (size class 32), optimal fields order:
struct {
y uint64
z *s
x uint32
t uint32
}Note
For applying suggested fix, use -apply flag, instead of -fix.
Development
Go 1.20+
Running test
Add test case to testdata/src/struct directory, then run:
go testContributing
TODO
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