cgen: implement overriding of != and ==

doc/docs.md

@@ -3166,11 +3166,11 @@ operator overloading is an important feature to have in order to improve readabi
 
 To improve safety and maintainability, operator overloading is limited:
 
-- It's only possible to overload `+, -, *, /, %, <, >` operators.
-- `==` and `!=` are self generated by the compiler.
+- It's only possible to overload `+, -, *, /, %, <, >, ==, !=` operators.
+- `==` and `!=` are self generated by the compiler but can be overriden.
 - Calling other functions inside operator functions is not allowed.
 - Operator functions can't modify their arguments.
-- When using `<` and `>`, the return type must be `bool`.
+- When using `<`, `>`, `==` and `!=` operators, the return type must be `bool`.
 - Both arguments must have the same type (just like with all operators in V).
 
 ## Inline assembly

vlib/v/ast/str.v

@@ -52,7 +52,7 @@ pub fn (node &FnDecl) stringify(t &table.Table, cur_mod string, m2a map[string]s
 		}
 	}
 	f.write('fn $receiver$name')
-	if name in ['+', '-', '*', '/', '%', '<', '>'] {
+	if name in ['+', '-', '*', '/', '%', '<', '>', '==', '!='] {
 		f.write(' ')
 	}
 	if node.is_generic {

vlib/v/checker/checker.v

@@ -4964,7 +4964,7 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			c.error('.str() methods should have 0 arguments', node.pos)
 		}
 	}
-	if node.language == .v && node.is_method && node.name in ['+', '-', '*', '%', '/', '<', '>'] {
+	if node.language == .v && node.is_method && node.name in ['+', '-', '*', '%', '/', '<', '>', '==', '!='] {
 		if node.params.len != 2 {
 			c.error('operator methods should have exactly 1 argument', node.pos)
 		} else {
@@ -4976,7 +4976,7 @@ fn (mut c Checker) fn_decl(mut node ast.FnDecl) {
 			} else {
 				if node.receiver.typ != node.params[1].typ {
 					c.error('both sides of an operator must be the same type', node.pos)
-				} else if node.name in ['<', '>'] && node.return_type != table.bool_type {
+				} else if node.name in ['<', '>', '==', '!='] && node.return_type != table.bool_type {
 					c.error('operator comparison methods should return `bool`', node.pos)
 				}
 			}

vlib/v/gen/cgen.v

@@ -2868,6 +2868,8 @@ fn (mut g Gen) infix_expr(node ast.InfixExpr) {
 		return
 	}
 	right_sym := g.table.get_type_symbol(node.right_type)
+	has_eq_overloaded := !right_sym.has_method('==') && !left_sym.has_method('==')
+	has_ne_overloaded := !right_sym.has_method('!=') && !left_sym.has_method('!=')
 	unaliased_right := if right_sym.kind == .alias {
 		(right_sym.info as table.Alias).parent_type
 	} else {
@@ -3006,7 +3008,8 @@ fn (mut g Gen) infix_expr(node ast.InfixExpr) {
 		}
 		g.expr(node.right)
 		g.write(')')
-	} else if node.op in [.eq, .ne] && left_sym.kind == .struct_ && right_sym.kind == .struct_ {
+	} else if node.op in [.eq, .ne] &&
+		left_sym.kind == .struct_ && right_sym.kind == .struct_ && has_eq_overloaded && has_ne_overloaded {
 		ptr_typ := g.gen_struct_equality_fn(left_type)
 		if node.op == .eq {
 			g.write('${ptr_typ}_struct_eq(')
@@ -3154,13 +3157,16 @@ fn (mut g Gen) infix_expr(node ast.InfixExpr) {
 		g.write(')')
 	} else {
 		a := (left_sym.name[0].is_capital() || left_sym.name.contains('.')) &&
-			left_sym.kind != .enum_
+			left_sym.kind !in [.enum_, .function, .interface_, .sum_type]
 		b := left_sym.kind != .alias
 		c := left_sym.kind == .alias && (left_sym.info as table.Alias).language == .c
 		// Check if aliased type is a struct
 		d := !b &&
 			g.typ((left_sym.info as table.Alias).parent_type).split('__').last()[0].is_capital()
-		if node.op in [.plus, .minus, .mul, .div, .mod, .lt, .gt] && ((a && b) || c || d) {
+		// Do not generate operator overloading with these `right_sym.kind`.
+		e := right_sym.kind !in [.voidptr, .any_int, .int]
+		if node.op in [.plus, .minus, .mul, .div, .mod, .lt, .gt, .eq, .ne] &&
+			((a && b && e) || c || d) {
 			// Overloaded operators
 			g.write(g.typ(if !d {
 				left_type

vlib/v/gen/fn.v

@@ -47,7 +47,7 @@ fn (mut g Gen) gen_fn_decl(it ast.FnDecl, skip bool) {
 	}
 	//
 	mut name := it.name
-	if name[0] in [`+`, `-`, `*`, `/`, `%`, `<`, `>`] {
+	if name in ['+', '-', '*', '/', '%', '<', '>', '==', '!='] {
 		name = util.replace_op(name)
 	}
 	if it.is_method {

vlib/v/parser/fn.v

@@ -270,7 +270,8 @@ fn (mut p Parser) fn_decl() ast.FnDecl {
 			}
 		}
 	}
-	if p.tok.kind in [.plus, .minus, .mul, .div, .mod, .gt, .lt] && p.peek_tok.kind == .lpar {
+	if p.tok.kind in [.plus, .minus, .mul, .div, .mod, .gt, .lt, .eq, .ne] &&
+		p.peek_tok.kind == .lpar {
 		name = p.tok.kind.str() // op_to_fn_name()
 		if rec_type == table.void_type {
 			p.error_with_pos('cannot use operator overloading with normal functions',

vlib/v/tests/operator_overloading_with_string_interpolation_test.v

@@ -35,6 +35,14 @@ fn (a Vec) < (b Vec) bool {
 	return a.x < b.x && a.y < b.y
 }
 
+fn (a Vec) == (b Vec) bool {
+	return a.x == b.y && a.y == b.x
+}
+
+fn (a Vec) != (b Vec) bool {
+	return !(a == b)
+}
+
 fn test_operator_overloading_with_string_interpolation() {
 	a := Vec{2, 3}
 	b := Vec{4, 5}
@@ -60,6 +68,8 @@ fn test_operator_overloading_with_string_interpolation() {
 	////// /////
 	assert b > a == true
 	assert a < b == true
+	assert (Vec{2, 3} == Vec{3, 2}) == true
+	assert (Vec{2, 3} != Vec{3, 2}) == false
 	////// /////
 	assert c.str() == '{6, 8}'
 	assert d.str() == '{-2, -2}'

vlib/v/util/util.v

@@ -278,18 +278,27 @@ pub fn imax(a int, b int) int {
 }
 
 pub fn replace_op(s string) string {
-	last_char := s[s.len - 1]
-	suffix := match last_char {
-		`+` { '_plus' }
-		`-` { '_minus' }
-		`*` { '_mult' }
-		`/` { '_div' }
-		`%` { '_mod' }
-		`<` { '_lt' }
-		`>` { '_gt' }
-		else { '' }
-	}
-	return s[..s.len - 1] + suffix
+	if s.len == 1 {
+		last_char := s[s.len - 1]
+		suffix := match last_char {
+			`+` { '_plus' }
+			`-` { '_minus' }
+			`*` { '_mult' }
+			`/` { '_div' }
+			`%` { '_mod' }
+			`<` { '_lt' }
+			`>` { '_gt' }
+			else { '' }
+		}
+		return s[..s.len - 1] + suffix
+	} else {
+		suffix := match s {
+			'==' { '_eq' }
+			'!=' { '_ne' }
+			else { '' }
+		}
+		return s[..s.len - 2] + suffix
+	}
 }
 
 pub fn join_env_vflags_and_os_args() []string {