From 570a7aaaf3e06a078248bed7cd6188f91ad85a0b Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Sat, 26 Oct 2019 21:58:26 +0300
Subject: [PATCH] a[start..end] slicing

---
 vlib/compiler/gen_c.v  | 18 ++++++++++++------
 vlib/compiler/gen_js.v |  2 +-
 vlib/compiler/parser.v | 24 ++++++++++++++++++++----
 3 files changed, 33 insertions(+), 11 deletions(-)

diff --git a/vlib/compiler/gen_c.v b/vlib/compiler/gen_c.v
index 62a2922790..03554b7efc 100644
--- a/vlib/compiler/gen_c.v
+++ b/vlib/compiler/gen_c.v
@@ -169,7 +169,7 @@ fn types_to_c(types []Type, table &Table) string {
 	return sb.str()
 }
 
-fn (p mut Parser) index_get(typ string, fn_ph int, cfg IndexCfg) {
+fn (p mut Parser) index_get(typ string, fn_ph int, cfg IndexConfig) {
 	// Erase var name we generated earlier:	"int a = m, 0"
 	// "m, 0" gets killed since we need to start from scratch. It's messy.
 	// "m, 0" is an index expression, save it before deleting and insert later in map_get()
@@ -195,15 +195,21 @@ fn (p mut Parser) index_get(typ string, fn_ph int, cfg IndexCfg) {
 			p.gen('$index_expr ]')
 		}
 		else {
-			if cfg.is_ptr {
-				p.gen('( *($typ*) array_get(* $index_expr) )')
-			}  else {
-				p.gen('( *($typ*) array_get($index_expr) )')
+			amp := if cfg.is_ptr { '&' } else { '' }
+			if cfg.is_slice {
+				p.gen(' array_slice($amp $index_expr) ')
+			}	
+			else {
+				p.gen('( *($typ*) array_get($amp $index_expr) )')
 			}
 		}
 	}
 	else if cfg.is_str && !p.builtin_mod {
-		p.gen('string_at($index_expr)')
+		if cfg.is_slice {
+			p.gen('string_substr($index_expr)')
+		} else {
+			p.gen('string_at($index_expr)')
+		}
 	}
 	// Zero the string after map_get() if it's nil, numbers are automatically 0
 	// This is ugly, but what can I do without generics?
diff --git a/vlib/compiler/gen_js.v b/vlib/compiler/gen_js.v
index 9c3718f790..14278674b0 100644
--- a/vlib/compiler/gen_js.v
+++ b/vlib/compiler/gen_js.v
@@ -70,7 +70,7 @@ fn types_to_c(types []Type, table &Table) string {
 	return sb.str()
 }
 
-fn (p mut Parser) index_get(typ string, fn_ph int, cfg IndexCfg) {
+fn (p mut Parser) index_get(typ string, fn_ph int, cfg IndexConfig) {
 	p.cgen.cur_line = p.cgen.cur_line.replace(',', '[') + ']'
 }
 
diff --git a/vlib/compiler/parser.v b/vlib/compiler/parser.v
index c4844f3cf1..2dd78e6667 100644
--- a/vlib/compiler/parser.v
+++ b/vlib/compiler/parser.v
@@ -2091,6 +2091,7 @@ fn (p mut Parser) index_expr(typ_ string, fn_ph int) string {
 	is_arr0 := typ.starts_with('array_')
 	is_arr := is_arr0 || typ == 'array'
 	is_ptr := typ == 'byte*' || typ == 'byteptr' || typ.contains('*')
+	mut is_slice := false
 	is_indexer := p.tok == .lsbr
 	mut close_bracket := false
 	index_error_tok_pos := p.token_idx
@@ -2163,6 +2164,19 @@ fn (p mut Parser) index_expr(typ_ string, fn_ph int) string {
 			if p.cgen.cur_line.right(index_pos).replace(' ', '').int() < 0 {
 				p.error('cannot access negative array index')
 			}
+			if p.tok == .dotdot {
+				if is_arr {
+					typ = 'array_' + typ
+				} else if is_str {
+					typ = 'string'
+				}	 else {
+					p.error('slicing is supported by arrays and strings only')
+				}	
+				is_slice = true
+				p.next()
+				p.gen(',')
+				p.check_types(p.expression(), 'int')
+			}	
 		}
 		else {
 			T := p.table.find_type(p.expression())
@@ -2197,6 +2211,7 @@ fn (p mut Parser) index_expr(typ_ string, fn_ph int) string {
 			return typ
 		}
 	}
+	// `m[key] = val`
 	// TODO move this from index_expr()
 	if (p.tok == .assign && !p.is_sql) || p.tok.is_assign() {
 		if is_indexer && is_str && !p.builtin_mod {
@@ -2216,26 +2231,27 @@ fn (p mut Parser) index_expr(typ_ string, fn_ph int) string {
 	// else if p.pref.is_verbose && p.assigned_var != '' {
 	// p.error('didnt assign')
 	// }
-	// m[key]. no =, just a getter
+	// `m[key]`. no =, just a getter
 	else if (is_map || is_arr || (is_str && !p.builtin_mod)) && is_indexer {
-		p.index_get(typ, fn_ph, IndexCfg{
+		p.index_get(typ, fn_ph, IndexConfig{
 			is_arr: is_arr
 			is_map: is_map
 			is_ptr: is_ptr
 			is_str: is_str
+			is_slice: is_slice
 		})
 	}
 	// else if is_arr && is_indexer{}
 	return typ
 }
 
-struct IndexCfg {
+struct IndexConfig {
 	is_map bool
 	is_str bool
 	is_ptr bool
 	is_arr bool
 	is_arr0 bool
-
+	is_slice bool
 }
 
 // for debugging only