Optimize CONCATENATE LINES OF runtime path

packages/runtime/src/statements/concatenate.ts

@@ -28,18 +28,22 @@ export function concatenate(input: IConcatenateInput) {
   }
 
   if (input.lines === true) {
-    const list: string[] = [];
+    let result = "";
     const tab = input.source[0];
     if (tab instanceof Table) {
-      for (const l of tab.array()) {
-        if (input.respectingBlanks !== true) {
-          list.push(l.get().trimEnd());
-        } else {
-          list.push(l.get());
+      const array = tab.array();
+      const length = array.length;
+      const respectingBlanks = input.respectingBlanks === true;
+      const hasSeparator = sep.length > 0;
+      for (let i = 0; i < length; i++) {
+        if (hasSeparator === true && i > 0) {
+          result += sep;
         }
+        const value = array[i].get();
+        result += respectingBlanks === true ? value : value.trimEnd();
       }
     }
-    input.target.set(list.join(sep));
+    input.target.set(result);
 
   } else {
     let result = "";

performance/index.ts

@@ -45,6 +45,7 @@ import {test39} from "./test39";
 import {test40} from "./test40";
 import {test41} from "./test41";
 import {test42} from "./test42";
+import {test43} from "./test43";
 
 // NOTE: does not run via Mocha
 
@@ -102,6 +103,7 @@ const tests: Tests = [
   {name: "40: eq string", abap: test40},
   {name: "41: eq char, different lengths", abap: test41},
   {name: "42: eq int with numc", abap: test42},
+  {name: "43: CONCATENATE LINES OF", abap: test43},
 ];
 
 async function execute(t: Test) {

performance/test43.ts

@@ -0,0 +1,12 @@
+export const test43 = `
+DATA lt_tab TYPE STANDARD TABLE OF string WITH DEFAULT KEY.
+DATA lv_str TYPE string.
+
+DO 2000 TIMES.
+  APPEND 'foobar' TO lt_tab.
+ENDDO.
+
+DO 1000 TIMES.
+  CONCATENATE LINES OF lt_tab INTO lv_str SEPARATED BY ','.
+ENDDO.
+`;

test/statements/concatenate.ts

@@ -161,6 +161,46 @@ WRITE count.`;
     expect(abap.console.get()).to.equal("5");
   });
 
+  it("CONCATENATE LINES OF, empty table", async () => {
+    const code = `
+DATA lt_tab TYPE STANDARD TABLE OF string WITH DEFAULT KEY.
+DATA res TYPE string.
+res = 'foo'.
+CONCATENATE LINES OF lt_tab INTO res SEPARATED BY '-'.
+ASSERT res IS INITIAL.`;
+    const js = await run(code);
+    const f = new AsyncFunction("abap", js);
+    await f(abap);
+  });
+
+  it("CONCATENATE LINES OF, single line", async () => {
+    const code = `
+DATA lt_tab TYPE STANDARD TABLE OF string WITH DEFAULT KEY.
+DATA res TYPE string.
+APPEND 'foo' TO lt_tab.
+CONCATENATE LINES OF lt_tab INTO res SEPARATED BY '--'.
+ASSERT res = 'foo'.`;
+    const js = await run(code);
+    const f = new AsyncFunction("abap", js);
+    await f(abap);
+  });
+
+  it("CONCATENATE LINES OF, char table, trailing blanks removed", async () => {
+    const code = `
+TYPES char5 TYPE c LENGTH 5.
+DATA lt_tab TYPE STANDARD TABLE OF char5 WITH DEFAULT KEY.
+DATA res TYPE string.
+APPEND 'ab' TO lt_tab.
+APPEND 'cd' TO lt_tab.
+CONCATENATE LINES OF lt_tab INTO res SEPARATED BY '--'.
+ASSERT res = 'ab--cd'.
+CONCATENATE LINES OF lt_tab INTO res.
+ASSERT res = 'abcd'.`;
+    const js = await run(code);
+    const f = new AsyncFunction("abap", js);
+    await f(abap);
+  });
+
   it("Separated by INTF constant", async () => {
     const code = `
 INTERFACE lif.