[swift-users] while case and if case usage

[Ramakrishna Mallireddy]

An example for illustration:

enum Test {

  case None

  case Integer(Int)

  case StringValue(String)

  case Addition(Int, Int)

}

func test(a:Test) {



  switch a {

  case .None: print(a)

  case .Integer(let value) where value > 50: print(value)

  case .StringValue: print(a)

  case .Addition(let operands): print(operands.0 + operands.1)

  default: print(a)

  }



  if case .None = a {

    print(a)

  }



  if case .Integer = a {

    print(a)

  }



  if case .Integer(let value) = a where value > 50 {

    print(value)

  }



  if case .Addition(let operands) = a  {

    print(operands.0 + operands.1)

  }



  if case .StringValue = a {

    print(a)

  }

}


test(Test.StringValue("Hello")) // StringValue("Hello")

test(Test.Integer(70)) // 70 & Integer(70) & 70

test(Test.Addition(10, -20)) // -10 & -10

On Wed, Feb 24, 2016 at 12:51 PM, Ramakrishna Mallireddy <
ramakrishna.malli at gmail.com> wrote:

> I find the swift grammar at the end of Swift Book very useful. This is the
> first time I have read a programming language grammar and I really felt why
> I haven't done this for my earlier programming languages. For couple of
> months I have just read the Language guide about using general constructs
> of swift language, but after reading the grammar and implemented a lexer &
> scanner(i.e parser, still in development) in swift my understanding of
> swift syntax is very good.
>
> Initially it was difficult to understand some parts of the grammar and its
> terminology as it was mostly used in compiler development. but apple really
> made it easy as there are no left recursive terminals.
> Hence forth I decided to first learn the grammar along with its construct
> guide for any language I am going to learn in the feature.
>
> The Swift Programming Language book Pages: 848 & 852 explains the if and
> case-condition clause syntax.
>
> Note: ‹› stands for optional syntax.
>
> Excerpt From: Apple Inc. “The Swift Programming Language (Swift 2.1).”
> iBooks. https://itun.es/in/jEUH0.l
>
> *If syntax:*
>   “if *condition-clause* code-block ‹else-clause›”
>
> *case-condition*: (is a condition-clause, along with others)
>  "case pattern initializer ‹where-clause›"
>
> Once you understand how to deal with the grammar, then you won't search
> for language construct example or tutorials.
>
> On Wed, Feb 24, 2016 at 11:56 AM, Ramakrishna Mallireddy <
> ramakrishna.malli at gmail.com> wrote:
>
>> I am not sure if this helps, This is how I understand it.
>>
>> what happens when you use normal switch.
>>
>> switch someEnumExpression {
>>  case someEnum.Element1: execute block / statements
>>  default: executeDefault
>> }
>>
>> // it checks each case with someEnumExpression, and if true then run it,
>> may be actual implementation might use dictionary with someEnum as Key
>> if case someEnum.Element1 == someEnumExpression {
>>   execute block / statements
>> } else {
>>   executeDefault
>> }
>>
>> unroll your switch to if's, then I am sure you will understand its
>> construct...but why swift provide this control branch statements with case,
>> because at time I am sure that or only want to check an expression is of
>> particular enum case, then I use the if case like above. while is similar.
>>
>> I am sorry if my explanation is vague.
>>
>>
>> On Wed, Feb 24, 2016 at 10:49 AM, Thomas# Chiang via swift-users <
>> swift-users at swift.org> wrote:
>>
>>> have any document explain about "while case" and "if case" ? thank you ~
>>>
>>> TMS#
>>>
>>> _______________________________________________
>>> swift-users mailing list
>>> swift-users at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-users
>>>
>>>
>>
>
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