Compile performance.md examples in tests

doc/performance.md

@@ -77,7 +77,9 @@ without bound:
 
   ```c++
   dom::parser parser(0); // This parser will refuse to automatically grow capacity
-  parser.set_capacity(1024*1024); // This allocates enough capacity to handle documents <= 1MB
+  simdjson::error_code allocate_error = parser.set_capacity(1024*1024); // This allocates enough capacity to handle documents <= 1MB
+  if (allocate_error) { cerr << allocate_error << endl; exit(1); }
+
   for (web_request request : listen()) {
     auto [doc, error] = parser.parse(request.body);
     // If the document was above our limit, emit 413 = payload too large

tests/readme_examples.cpp

@@ -93,6 +93,49 @@ void implementation_selection_4() {
   simdjson::active_implementation = simdjson::available_implementations["fallback"];
 }
 
+void performance_1() {
+  dom::parser parser;
+
+  // This initializes buffers and a document big enough to handle this JSON.
+  dom::element doc = parser.parse("[ true, false ]"_padded);
+  cout << doc << endl;
+
+  // This reuses the existing buffers, and reuses and *overwrites* the old document
+  doc = parser.parse("[1, 2, 3]"_padded);
+  cout << doc << endl;
+
+  // This also reuses the existing buffers, and reuses and *overwrites* the old document
+  dom::element doc2 = parser.parse("true"_padded);
+  // Even if you keep the old reference around, doc and doc2 refer to the same document.
+  cout << doc << endl;
+  cout << doc2 << endl;
+}
+
+// The web_request part of this is aspirational, so we compile as much as we can here
+void performance_2() {
+  dom::parser parser(1024*1024); // Never grow past documents > 1MB
+//   for (web_request request : listen()) {
+    auto [doc, error] = parser.parse("1"_padded/*request.body*/);
+//     // If the document was above our limit, emit 413 = payload too large
+    if (error == CAPACITY) { /* request.respond(413); continue; */ }
+//     // ...
+//   }
+}
+
+// The web_request part of this is aspirational, so we compile as much as we can here
+void performance_3() {
+  dom::parser parser(0); // This parser will refuse to automatically grow capacity
+  simdjson::error_code allocate_error = parser.set_capacity(1024*1024); // This allocates enough capacity to handle documents <= 1MB
+  if (allocate_error) { cerr << allocate_error << endl; exit(1); }
+
+  // for (web_request request : listen()) {
+    auto [doc, error] = parser.parse("1"_padded/*request.body*/);
+    // If the document was above our limit, emit 413 = payload too large
+    if (error == CAPACITY) { /* request.respond(413); continue; */ }
+    // ...
+  // }
+}
+
 int main() {
   return 0;
 }