You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: icu.go
    path of file: ./repos/gotosocial/vendor/golang.org/x/text/cases
    
    the code of the file until where you have to start completion: // Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

//go:build icu

package cases

// Ideally these functions would be defined in a test file, but go test doesn't
// allow CGO in tests. The build tag should ensure either way that these
// functions will not end up in the package.

// TODO: Ensure that the correct ICU version is set.

/*
#cgo LDFLAGS: -licui18n.57 -licuuc.57
#include <stdlib.h>
#include <unicode/ustring.h>
#include <unicode/utypes.h>
#includ
    
func doICU(tag, caser, input string) string {
	err := C.UErrorCode(0)
	loc := C.CString(tag)
	cm := C.ucasemap_open(loc, C.uint32_t(0), &err)

	buf := make([]byte, len(input)*4)
	dst := (*C.char)(unsafe.Pointer(&buf[0]))
	src := C.CString(input)

	cn := C.int32_t(0)

	switch caser {
	case "fold":
		cn = C.ucasemap_utf8FoldCase(cm,
			dst, C.int32_t(len(buf)),
			src, C.int32_t(len(input)),
			&err)
	case "lower":
		cn = C.ucasemap_utf8ToLower(cm,
			dst, C.int32_t(len(buf)),
			src, C.int32_t(len(input)),
			&err)
	case "upper":
		cn = C.ucasemap_utf8ToUpper(cm,
			dst, C.int32_t(len(buf)),
			src, C.int32_t(len(input)),
			&err)
	case "title":
		cn = C.ucasemap_utf8ToTitle(cm,
			dst, C.int32_t(len(buf)),
			src, C.int32_t(len(input)),
			&err)
	}
	return string(buf[:cn])
}