Implement String#slice (#404)

std/assembly/index.d.ts

@@ -682,6 +682,7 @@ declare class String {
   padStart(targetLength: i32, padString?: string): string;
   padEnd(targetLength: i32, padString?: string): string;
   repeat(count?: i32): string;
+  slice(beginIndex: i32, endIndex?: i32): string;
   split(separator?: string, limit?: i32): string[];
   toString(): string;
   static fromUTF8(ptr: usize, len: usize): string;

std/assembly/string.ts

@@ -413,6 +413,17 @@ export class String {
     return result;
   }
 
+  slice(beginIndex: i32, endIndex: i32 = i32.MAX_VALUE): String {
+    var length = this.length;
+    var begin = (beginIndex < 0) ? max(beginIndex + length, 0) : min(beginIndex, length);
+    var end = (endIndex < 0) ? max(endIndex + length, 0) : min(endIndex, length);
+    var len = end - begin;
+    if (len <= 0) return changetype<String>("");
+    var out = allocateUnsafe(len);
+    copyUnsafe(out, 0, this, begin, len);
+    return out;
+  }
+
   split(separator: String = null, limit: i32 = i32.MAX_VALUE): String[] {
     assert(this !== null);
     if (!limit) return new Array<String>();

std/portable/index.d.ts

@@ -427,6 +427,7 @@ declare class String {
   padEnd(targetLength: i32, padString?: string): string;
   replace(search: string, replacement: string): string;
   repeat(count?: i32): string;
+  slice(beginIndex: i32, endIndex?: i32): string;
   split(separator?: string, limit?: i32): string[];
   toString(): string;
 }

tests/compiler/std/string-utf8.optimized.wat

@@ -1575,7 +1575,7 @@
       if
        i32.const 0
        i32.const 72
-       i32.const 510
+       i32.const 521
        i32.const 8
        call $~lib/env/abort
        unreachable
@@ -1622,7 +1622,7 @@
        if
         i32.const 0
         i32.const 72
-        i32.const 514
+        i32.const 525
         i32.const 8
         call $~lib/env/abort
         unreachable
@@ -1695,7 +1695,7 @@
        if
         i32.const 0
         i32.const 72
-        i32.const 526
+        i32.const 537
         i32.const 8
         call $~lib/env/abort
         unreachable
@@ -1748,7 +1748,7 @@
   if
    i32.const 0
    i32.const 72
-   i32.const 535
+   i32.const 546
    i32.const 4
    call $~lib/env/abort
    unreachable

tests/compiler/std/string-utf8.untouched.wat

@@ -2001,7 +2001,7 @@
         if
          i32.const 0
          i32.const 72
-         i32.const 510
+         i32.const 521
          i32.const 8
          call $~lib/env/abort
          unreachable
@@ -2055,7 +2055,7 @@
          if
           i32.const 0
           i32.const 72
-          i32.const 514
+          i32.const 525
           i32.const 8
           call $~lib/env/abort
           unreachable
@@ -2150,7 +2150,7 @@
          if
           i32.const 0
           i32.const 72
-          i32.const 526
+          i32.const 537
           i32.const 8
           call $~lib/env/abort
           unreachable
@@ -2213,7 +2213,7 @@
   if
    i32.const 0
    i32.const 72
-   i32.const 535
+   i32.const 546
    i32.const 4
    call $~lib/env/abort
    unreachable

tests/compiler/std/string.ts

@@ -4,7 +4,6 @@ import {
   itoa32,
   utoa64,
   itoa64,
-  itoa,
   dtoa
 } from "internal/number";
 
@@ -143,6 +142,16 @@ assert("a".repeat(5) == "aaaaa");
 assert("a".repeat(6) == "aaaaaa");
 assert("a".repeat(7) == "aaaaaaa");
 
+// test cases for slice method
+str = "abcdefghijklmn";
+assert(str.slice(0) == "abcdefghijklmn");
+assert(str.slice(-1) == "n");
+assert(str.slice(-5) == "jklmn");
+assert(str.slice(2, 7) == "cdefg");
+assert(str.slice(-11, -6) == "defgh");
+assert(str.slice(4, 3) == "");
+assert(str.slice(0, -1) == "abcdefghijklm");
+
 var sa: string[];
 
 sa = "".split();