Fix docs C++ snippet for the .fail() args

- Fix the wrong lambda format (missing `[]`).
- Make consistent argument naming (`error`).
- Use `const &` when appropriated.

docs/qtpromise/exceptions/canceled.md

@@ -7,7 +7,7 @@ canceled (e.g. using [`QFuture::cancel()`](http://doc.qt.io/qt-5/qfuture.html#ca
 
 ```cpp
 auto output = QtPromise::resolve(future)
-    .fail([](const QPromiseCanceledException&) {
+    .fail([](const QPromiseCanceledException& error) {
         // `future` has been canceled!
     });
 ```

docs/qtpromise/exceptions/timeout.md

@@ -8,7 +8,7 @@ This is the default exception thrown when reaching the time limit when using the
 ```cpp
 QPromise<int> input = {...}
 auto output = input.timeout(2000)
-    .fail([](const QPromiseTimeoutException& e) {
+    .fail([](const QPromiseTimeoutException& error) {
         // operation timed out after 2s!
     });
 ```

docs/qtpromise/getting-started.md

@@ -90,9 +90,9 @@ download(url).then(&uncompress).then([](const Entries& entries) {
     // {...} process entries
 }).finally([]() {
     // {...} cleanup
-}).fail([](QNetworkReply::NetworkError err) {
+}).fail([](QNetworkReply::NetworkError error) {
     // {...} handle network error
-}).fail([](const UpdateException& err) {
+}).fail([](const UpdateException& error) {
     // {...} handle update error
 }).fail([]() {
     // {...} catch all

docs/qtpromise/helpers/attempt.md

@@ -41,7 +41,7 @@ auto output = process(url);
 // 'output' type: QPromise<QByteArray>
 output.then([](const QByteArray& res) {
     // {...}
-}).fail([](const InvalidUrlException& err) {
+}).fail([](const InvalidUrlException& error) {
     // {...}
 });
 ```

docs/qtpromise/helpers/connect.md

@@ -42,9 +42,9 @@ auto output = QtPromise::connect(sender, &Sender::finished, &Sender::error);
 // 'output' type: QPromise<QByteArray>
 output.then([](const QByteArray& res) {
     // 'res' is the first argument of the 'finished' signal.
-}).fail([](ErrorCode err) {
+}).fail([](ErrorCode error) {
-    // 'err' is the first argument of the 'error' signal.
+    // 'error' is the first argument of the 'error' signal.
-}).fail([](const QPromiseContextException& err) {
+}).fail([](const QPromiseContextException& error) {
     // the 'sender' object has been destroyed before any of
     // the 'finished' or 'error' signals have been emitted.
 });

docs/qtpromise/qpromise/fail.md

@@ -10,16 +10,19 @@ title: .fail
 QPromise<T>::fail(Function onRejected) -> QPromise<T>
 ```
 
-Shorthand to `promise.then(nullptr, onRejected)`, similar to the [`catch` statement](http://en.cppreference.com/w/cpp/language/try_catch):
+Shorthand to [`promise.then(nullptr, onRejected)`](then.md) for handling errors in promise chains,
+similar to the native C++ [`catch` statement](http://en.cppreference.com/w/cpp/language/try_catch):
 
 ```cpp
-promise.fail([](const MyException&) {
+promise.fail([](const MyException& error) {
     // {...}
-}).fail(const QException&) {
+}).fail([](const QException& error) {
     // {...}
-}).fail(const std::exception&) {
+}).fail([](const std::exception& error) {
     // {...}
-}).fail() {
+}).fail([]() {
     // {...} catch-all
 });
 ```
+
+See also: [`QPromise::then`](then.md)

docs/qtpromise/qpromise/tapfail.md

@@ -17,12 +17,12 @@ rejected with the new exception.
 
 ```cpp
 QPromise<int> input = {...}
-auto output = input.tapFail([](Error err) {
+auto output = input.tapFail([](const Error& error) {
-    log(err);
+    log(error);
 }).then([](int res) {
     return process(res);
-}).fail([](Error err) {
+}).fail([](const Error& error) {
-    handle(err);
+    handle(error);
     return -1;
 });
 ```

docs/qtpromise/qpromise/timeout.md

@@ -21,7 +21,7 @@ auto output = input.timeout(2000)
     .then([](int res) {
         // operation succeeded within 2 seconds
     })
-    .fail([](const QPromiseTimeoutException& e) {
+    .fail([](const QPromiseTimeoutException& error) {
         // operation timed out!
     });
 ```

docs/qtpromise/qtconcurrent.md

@@ -67,7 +67,7 @@ promise.then([](int res) {
 
         return QString("42");
     });
-}).fail(const CustomException& err) {
+}).fail([](const CustomException& error) {
     // {...}
 });
 ```

docs/qtpromise/qtsignals.md

@@ -53,7 +53,7 @@ auto output = QtPromise::connect(obj, &Object::finished, &Object::error);
 // output type: QPromise<QByteArray>
 output.then([](const QByteArray& data) {
     // {...}
-}).fail(const ObjectError& error) {
+}).fail([](const ObjectError& error) {
     // {...}
 });
 ```
@@ -69,7 +69,7 @@ auto output = QtPromise::connect(obj, &Object::finished, &Object::error);
 // output type: QPromise<QByteArray>
 output.then([]() {
     // {...}
-}).fail(const QPromiseUndefinedException& error) {
+}).fail([](const QPromiseUndefinedException& error) {
     // {...}
 });
 ```
@@ -84,7 +84,7 @@ auto output = QtPromise::connect(objA, &ObjectA::finished, objB, &ObjectB::error
 // output type: QPromise<QByteArray>
 output.then([](const QByteArray& data) {
     // {...}
-}).fail(const ObjectBError& error) {
+}).fail([](const ObjectBError& error) {
     // {...}
 });
 ```