Some code improvements

[sosiska]

• strings.ToLower comparison changed to strings.EqualFold.
• Rewrite switch statement with only one case as if.

[codecov]

Codecov Report

Merging #1909 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1909      +/-   ##
==========================================
- Coverage   98.74%   98.74%   -0.01%     
==========================================
  Files          38       38              
  Lines        2147     2145       -2     
==========================================
- Hits         2120     2118       -2     
  Misses         15       15              
  Partials       12       12

Impacted Files	Coverage Δ
context.go	98.36% <100%> (ø)	⬆️
binding/form_mapping.go	100% <100%> (ø)	⬆️
tree.go	100% <100%> (ø)	⬆️

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[appleboy]

Good Catch. some benchmark result:

package main

import (
	"strings"
	"testing"
)

var EqualFoldTests = []struct {
	s, t string
	out  bool
}{
	{"abc", "abc", true},
	{"ABcd", "ABcd", true},
	{"123abc", "123ABC", true},
	{"αβδ", "ΑΒΔ", true},
	{"abc", "xyz", false},
	{"abc", "XYZ", false},
	{"abcdefghijk", "abcdefghijX", false},
	{"abcdefghijk", "abcdefghij\u212A", true},
	{"abcdefghijK", "abcdefghij\u212A", true},
	{"abcdefghijkz", "abcdefghij\u212Ay", false},
	{"abcdefghijKz", "abcdefghij\u212Ay", false},
	{"1", "2", false},
	{"utf-8", "US-ASCII", false},
}

func TestEqualFold(t *testing.T) {
	for _, tt := range EqualFoldTests {
		if out := strings.EqualFold(tt.s, tt.t); out != tt.out {
			t.Errorf("EqualFold(%#q, %#q) = %v, want %v", tt.s, tt.t, out, tt.out)
		}
		if out := strings.EqualFold(tt.t, tt.s); out != tt.out {
			t.Errorf("EqualFold(%#q, %#q) = %v, want %v", tt.t, tt.s, out, tt.out)
		}
	}
}

func BenchmarkToLower(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, tt := range EqualFoldTests {
			if out := (strings.ToLower(tt.s) == strings.ToLower(tt.t)); out != tt.out {
				b.Fatal("wrong result")
			}
		}
	}
}

func BenchmarkEqualFold(b *testing.B) {
	for i := 0; i < b.N; i++ {
		for _, tt := range EqualFoldTests {
			if out := strings.EqualFold(tt.s, tt.t); out != tt.out {
				b.Fatal("wrong result")
			}
		}
	}
}

result:

goos: darwin
goarch: amd64
pkg: 
BenchmarkToLower-8       1000000              1641 ns/op             208 B/op         13 allocs/op
BenchmarkEqualFold-8     3000000               481 ns/op               0 B/op          0 allocs/op
PASS