Golang—invalid operation: m[1] (type *string does not support indexing)

问题

invalid operation: m[1] (type *string does not support indexing)

错误复现

func TestStringPtr(t *testing.T){
    str := "this is a message"
    m := &str
    t.Log(*m[1])
}

// output
ouyangjun@:~/data/project/algorithm/leetcode/0010$go test -v -run="StringPtr"
# github.com/oyjjpp/algorithm/leetcode/0010 [github.com/oyjjpp/algorithm/leetcode/0010.test]
./0010_test.go:18:13: invalid operation: m[1] (type *string does not support indexing)
FAIL	github.com/oyjjpp/algorithm/leetcode/0010 [build failed]

原因

写代码第一印象str为“string”类型，m为“prt”类型，通过验证确实如理解所示

func TestStringPtr(t *testing.T){
    str := "this is a message"
    m := &str
    
    t.Log(reflect.ValueOf(m).Kind())
    t.Log(reflect.ValueOf(*m).Kind())
}
// output
=== RUN   TestStringPtr
    0010_test.go:18: ptr
    0010_test.go:19: string
--- PASS: TestStringPtr (0.00s)
PASS

但是输出结果却与理解不同，再去读一遍错误信息“invalid operation: m[1] (type *string does not support indexing” 很明显的错误啊，类型错误，”*m“明明是字符串类型啊，为什么不对呢？

重点，重点，重点 [关键点“m[1]” 操作符的优先级]

第一印象以为*m[1] m指针先转换为string再取值，实际是先通过m去取值，在转指针，所以报列上面错误

解决方案

使用“()”，改变优先级

func TestStringPtr(t *testing.T){
    str := "this is a message"
    m := &str
    
    t.Log(reflect.ValueOf(m).Kind())
    t.Log(reflect.ValueOf(*m).Kind())
    t.Log((*m)[1])
}