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diff --git a/objectivec/README.md b/objectivec/README.md index 186e45b2..134bf1ab 100644 --- a/objectivec/README.md +++ b/objectivec/README.md @@ -21,15 +21,15 @@ Installation ------------ The full distribution pulled from github includes the sources for both the -compiler (protoc) and the runtime (this directory). To build the compiler +compiler (protoc) and the runtime (this directory). To build the compiler and run the runtime tests, you can use: $ objectivec/DevTools/full_mac_build.sh This will generate the `src/protoc` binary. -Usage ------ +Building +-------- There are two ways to include the Runtime sources in your project: @@ -47,6 +47,80 @@ If the target is using ARC, remember to turn off ARC (`-fno-objc-arc`) for the The files generated by `protoc` for the `*.proto` files (`\*.pbobjc.h' and `\*.pbobjc.m`) are then also added to the target. +Usage +----- + +The objects generated for messages should work like any other Objective C +object. They are mutable objects, but if you don't change them, they are safe +to share between threads (similar to passing an NSMutableDictionary between +threads/queues; as long as no one mutates it, things are fine). + +There are a few behaviors worth calling out: + +A property that is type NSString\* will never return nil. If the value is +unset, it will return an empty string (@""). This is inpart to align things +with the Protocol Buffers spec which says the default for strings is an empty +string, but also so you can always safely pass them to isEqual:/compare:, etc. +and have deterministic results. + +A property that is type NSData\* also won't return nil, it will return an empty +data ([NSData data]). The reasoning is the same as for NSString not returning +nil. + +A property that is another GPBMessage class also will not return nil. If the +field wasn't already set, you will get a instance of the correct class. This +instance will be a temporary instance unless you mutate it, at which point it +will be attached to its parent object. We call this pattern *autocreators*. +Similar to NSString and NSData properties it makes things a little safer when +using them with isEqual:/etc.; but more importantly, this allows you to write +code that uses Objective C's property dot notation to walk into nested objects +and access and/or assign things without having to check that they are not nil +and create them each step along the way. You can write this: + +``` +- (void)updateRecord:(MyMessage *)msg { + ... + // Note: You don't have to check subMessage and otherMessage for nil and + // alloc/init/assign them back along the way. + msg.subMessage.otherMessage.lastName = @"Smith"; + ... +} +``` + +If you want to check if a GPBMessage property is present, there is always as +`has\[NAME\]` property to go with the main property to check if it is set. + +A property that is of an Array or Dictionary type also provides *autocreator* +behavior and will never return nil. This provides all the same benefits you +see for the message properties. Again, you can write: + +``` +- (void)updateRecord:(MyMessage *)msg { + ... + // Note: Just like above, you don't have to check subMessage and otherMessage + // for nil and alloc/init/assign them back along the way. You also don't have + // to create the siblingsArray, you can safely just append to it. + [msg.subMessage.otherMessage.siblingsArray addObject:@"Pat"]; + ... +} +``` + +If you are inspecting a message you got from some other place (server, disk, +etc), you may want to check if the Array or Dictionary has entries without +causing it to be created for you. For this, there is always a `\[NAME\]_Count` +property also provided that can return zero or the real count, but won't trigger +the creation. + +For primitive type fields (ints, floats, bools, enum) in messages defined in a +`.proto` file that use *proto2* syntax there are conceptual differences between +having an *explicit* and *default* value. You can always get the value of the +property. In the case that it hasn't been set you will get the default. In +cases where you need to know whether it was set explicitly or you are just +getting the default, you can use the `has\[NAME\]` property. If the value has +been set, and you want to clear it, you can set the `has\[NAME\]` to `NO`. +*proto3* syntax messages do away with this concept, thus the default values are +never included when the message is encoded. + The Objective C classes/enums can be used from Swift code. Objective C Generator Options @@ -55,18 +129,19 @@ Objective C Generator Options **objc_class_prefix=\<prefix\>** (no default) Since Objective C uses a global namespace for all of its classes, there can -be collisions. This option provides a prefix that will be added to the Enums -and Objects (for messages) generated from the proto. Convention is to base +be collisions. This option provides a prefix that will be added to the Enums +and Objects (for messages) generated from the proto. Convention is to base the prefix on the package the proto is in. Contributing ------------ Please make updates to the tests along with changes. If just changing the -runtime, the Xcode projects can be used to build and run tests. If change also -require changes to the generated code, `objectivec/DevTools/full_mac_build.sh` -can be used to easily rebuild and test changes. Passing `-h` to the script will -show the addition options that could be useful. +runtime, the Xcode projects can be used to build and run tests. If your change +also requires changes to the generated code, +`objectivec/DevTools/full_mac_build.sh` can be used to easily rebuild and test +changes. Passing `-h` to the script will show the addition options that could +be useful. Documentation ------------- |