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Simplified JsonVariant::as<T>() to always return T

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Benoit Blanchon
2021-03-08 09:58:09 +01:00
parent 9094179856
commit e4ce75e20c
16 changed files with 78 additions and 81 deletions
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31
CHANGELOG.md
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@@ -11,9 +11,12 @@ HEAD
* Added `JsonVariant::is<JsonArrayConst/JsonObjectConst>()` (issue #1412)
* Added `JsonVariant::is<JsonVariant/JsonVariantConst>()` (issue #1412)
* Changed `JsonVariantConst::is<JsonArray/JsonObject>()` to return `false` (issue #1412)
* Simplified `JsonVariant::as<T>()` to always return `T` (see below)
> ### BREAKING CHANGES
>
> #### Support for `char` removed
>
> We cannot cast a `JsonVariant` to a `char` anymore, so the following will break:
> ```c++
> char age = doc["age"]; // error: no matching function for call to 'variantAs(VariantData*&)'
@@ -34,13 +37,39 @@ HEAD
> doc["age"] = age; // OK
> ```
>
> #### `as<T>()` always returns `T`
>
> Previously, `JsonVariant::as<T>()` could return a type different from `T`.
> The most common example is `as<char*>()` that returned a `const char*`.
> While this feature simplified a few use cases, it was confusing and complicated the
> implementation of custom converters.
>
> Starting from this version, `as<T>` doesn't try to auto-correct the return type and always return `T`,
> which means that you cannot write this anymore:
>
> ```c++
> Serial.println(doc["sensor"].as<char*>()); // error: invalid conversion from 'const char*' to 'char*' [-fpermissive]
> ```
>
> Instead, you must write:
>
> ```c++
> Serial.println(doc["sensor"].as<const char*>()); // OK
> ```
>
>
> #### `DeserializationError::NotSupported` removed
>
> On a different topic, `DeserializationError::NotSupported` has been removed.
> Instead of returning this error:
>
> * `deserializeJson()` leaves `\uXXXX` unchanged (only when `ARDUINOJSON_DECODE_UNICODE` is `0`)
> * `deserializeMsgPack()` replaces unsupported values with `null`s
>
> Lastly, a very minor change conserns `JsonVariantConst::is<T>()`.
> #### Const-aware `is<T>()`
>
> Lastly, a very minor change concerns `JsonVariantConst::is<T>()`.
> It used to return `true` for `JsonArray` and `JsonOject`, but now it returns `false`.
> Instead, you must use `JsonArrayConst` and `JsonObjectConst`.