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Features[ edit ] This section may be too technical for most readers to understand.
Please help improve it to make it understandable to non-expertswithout removing the technical details. June Learn how and when to remove this template message Swift is an alternative to the Objective-C language that employs modern programming-language theory concepts and strives to present a simpler syntax.
During its introduction, it was described simply as "Objective-C without the baggage of C". Also, Objective-C's use of a Smalltalk -like syntax for making method calls has been replaced with a dot-notation style and namespace system more familiar to programmers from other common object-oriented OO languages like Java or C.
Swift introduces true named parameters and retains key Objective-C concepts, including protocolsclosures and categoriesoften replacing former syntax with cleaner versions and allowing these concepts to be applied to other language structures, like enumerated types enums  Swift supports closures known as lambdas in opțiune binară swft languages.
The parameter name of the first trailing closure must be omitted.
Swift (programming language)
The parameter names of the remaining trailing closures must not be omitted. If all the arguments given to a function are trailing opțiune binară swft, you may omit the parentheses after the function's name. Calls to a function with trailing closures must be parenthesized if used in a guard statement.
Objective-C provided various bits of syntactic sugar to allow some of these objects to be created on-the-fly within the language, but once created, the objects were manipulated with object calls.
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Unlike many object-oriented languages, these access controls ignore inheritance hierarchies: private indicates that a symbol is accessible only in the immediate scopefileprivate indicates it is accessible only from within the file, internal indicates it is accessible within the containing module, public indicates it is accessible from any module, and open only for classes and their methods indicates that the class may be subclassed outside of the module.
This implies that non-optional types cannot result in a null-pointer error ; the compiler can ensure this is not possible.
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As in C Swift also includes syntactic sugar for this, allowing one to indicate a variable is optional by placing a question mark after the type name, var optionalInteger: Int?. Optional types wrap the base type, resulting in a different instance.
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String and String? To access the value inside, assuming it is not nil, it must be unwrapped to expose the instance inside. This is performed with the! If anOptionalInstance is nil, a null-pointer error occurs.
Normally this requires the programmer to test whether myValue is nil before proceeding. While the syntax can act as an if statement, its primary benefit is inferring non-nullability.
Where an if statement requires a case, guard assumes the opțiune binară swft based on the condition provided. Also, since guard contains no scope, with exception informații bitcoin the else closure, leaseStart is presented as an unwrapped optional to the guard's super-scope. Lastly, if the guard statement's test fails, Swift requires the else to exit the current method or loop, ensuring leaseStart never is accessed when nil. This is performed with the keywords opțiune binară swft, continue, break, or throw, or by calling a function returning a Never e.
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Objective-C was weakly typed and allowed any method to be called on any object at any time. If the method call failed, there was a default handler in the runtime that returned nil.
However, this also demanded that all method calls be dynamic, which introduces significant overhead. Swift's use of optionals provides a similar mechanism for testing and dealing with nils, but does so in a way that allows the compiler to use static dispatch because the unwrapping action is called on a defined instance the wrapperversus occurring in opțiune binară swft runtime dispatch system.
Value types[ edit ] In many object-oriented languages, objects are represented internally in two parts. The object is stored as a block of data placed on the heapwhile the name or "handle" to that object is represented by a pointer. Objects are passed between methods by copying the value of the pointer, opțiune binară swft the same underlying data on the heap to be accessed by anyone with a copy.
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In contrast, basic types opțiune binară swft integers and floating-point values are represented directly; the handle contains the data, not a pointer to it, and that data is passed directly to methods by copying. These styles of access are termed pass-by-reference opțiune binară swft the case of objects, and pass-by-value for basic types.
Both concepts have their advantages and disadvantages. Objects are useful when the data is large, like the description of a window or the contents of a document. In these cases, access to that data is provided by copying a or bit value, versus copying an entire data structure. However, smaller values like integers are the same size as pointers typically both are one wordso there is no advantage to passing a pointer, versus passing the value.
Also, pass-by-reference inherently requires a dereferencing operation, which can produce noticeable overhead in some operations, typically those used with these basic value types, like mathematics. Similarly to C opțiune binară swft in contrast to most other OO languages,[ citation needed ] Swift offers built-in support for objects using either pass-by-reference or pass-by-value semantics, the former using the class declaration and the latter using struct.
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Structs in Swift have almost all the same features as classes: methods, implementing protocols and using the extension mechanisms. For this reason, Apple terms all data generically as instances, opțiune binară swft objects or values. Structs do not support inheritance, however. Larger structures like windows would be defined as classes, allowing them to be passed around as pointers. Smaller structures, like a 2D point, can be defined as structs, which will be pass-by-value and allow direct access to their internal data with no dereference.
The performance improvement inherent to the pass-by-value concept is such that Swift uses these types for almost all common data types, including Int and Double, and types normally represented by objects, like String and Array.
This means that the various accessors have what is in effect opțiune binară swft pointer to the same data storage. So while the data is physically stored as one instance in memory, at the level of the application, these values are separate and physical separation is enforced opțiune binară swft copy on write only if needed.
Categories allow extending classes in-place to add new functions with opțiune binară swft need to subclass or even have access to the original source code. An example might be to add spell checker support to the base Opțiune binară swft class, which means all instances of NSString in opțiune binară swft application gain spell checking.
The system is also widely used as an organizational technique, allowing related code to be gathered into library-like extensions.
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Swift continues to support this concept, although they are now termed opțiune binară swft, and declared with the keyword extension. Unlike Objective-C, Swift can also add new properties accessors, types, and enums to extant instances[ citation needed ].
Another key feature of Objective-C is its use of protocolsknown in most modern languages as interfaces. Protocols promise that a particular class implements a set of methods, meaning that other objects in the system can call those methods on any object supporting that protocol. This is often used in modern OO languages as a substitute for multiple inheritancealthough the feature sets are not entirely similar.
A opțiune binară swft example of a protocol in Cocoa is the NSCopying protocol, opțiune binară swft defines one method, copyWithZone, that implements deep copying on objects. Combined, these allow protocols to be written once and support a wide variety of instances. Also, the extension mechanism can be used to add protocol conformance to an object that does not list that protocol in its definition. As Swift treats structs and classes as similar concepts, both extensions and protocols are extensively used in Swift's runtime to provide a rich API based on structs.
A concrete example of how all of these features interact can be seen in the concept of default protocol implementations: func! Any instance, class or struct, automatically gains this implementation simply by conforming to Equatable. As many instances gain Equatable through their base implementations or other generic extensions, most basic objects in the runtime gain equals and not equals with no code. This concept is so widely used within Swift, that Apple has begun calling it a protocol-oriented programming language.
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They suggest addressing many of the problem domains normally solved through classes and inheritance using protocols and structs instead. It also depends on Grand Central Dispatch. This takes the form of an additional header file that simply defines or imports all of the Objective-C symbols that are needed by the project's Swift code.
At that point, Opțiune binară swft can refer to the types, functions, and variables declared in those imports as though they were written opțiune binară swft Swift. Objective-C code can also use Swift code directly, by importing an automatically maintained header file with Bani rapidi pentru studenți declarations of the project's Swift symbols.
Not all symbols are available through this mechanism, however—use of Swift-specific features like generic types, opțiune binară swft optional types, sophisticated enums, or even Unicode identifiers may render a symbol inaccessible from Objective-C. Like Objective-C, attributes use the syntax, but the currently available set is small. One example is the IBOutlet attribute, which marks a given value in the code as an outlet, available for use within Interface Builder IB.
An outlet is a device that binds the value of the on-screen display to an object in code. On non-Apple systems, Swift does not depend on an Objective-C runtime or other Apple system libraries; a set of Swift "Corelib" implementations replace them.
Apple used to require manual memory management in Opțiune binară swft, but introduced ARC in to allow for easier memory allocation and deallocation. A references B, B references A. This causes them to become leaked into memory as they are never released. Swift provides the keywords weak and unowned to prevent strong reference cycles.
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Typically a parent-child relationship would use a strong opțiune binară swft while a child-parent would use either weak reference, where parents and children can be unrelated, or strategia de opțiuni binare 10 din 10 where a child always has a parent, but parent may not have a opțiune binară swft. Weak references must be optional variables, since they can change and become nil.
Self references to be treated as weak or unowned can be indicated using a capture list. Debugging and other elements[ edit ] A key element opțiune binară swft the Swift system is its opțiune binară swft to be cleanly debugged and run within the development environment, using a read—eval—print loop REPLgiving it interactive properties more in common with the scripting abilities of Python than traditional system programming languages.
The REPL is further enhanced with the new concept playgrounds.