Limited import clarification and its effect/tryswift2019

Import is able to explicitly specify submodules or specific elements.In this session, I will review the specifications of these imports and consider the impact on binary size and performance.

Transcript

1. Limited import clarification
   and its effect
   try! Swift Tokyo 2019
   Tomoya Hirano @DeNA
   

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2. Import
   

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3. Import Declaration
   1. attributes import module
   2. attributes import module.submodule
   3. attributes import importKind module.symbolName
   

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4. Import Declaration
   1. attributes import module
   2. attributes import module.submodule
   3. attributes import importKind module.symbolName
   

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5. 1. Attributes
   • Specify how to import symbols
   
   • Optional
   
   • @testable / @_exported
   

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6. @testable
   • For testing and development.
   
   • Import internal methods as public.
   

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7. @_exported
   • Import symbols as own code
   
   • Undocumented attributes
   

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8. 2. Submodule import
   1. attributes import module
   2. attributes import module.submodule
   3. attributes import importKind module.symbolName
   

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9. Example: SceneKit initializer
   

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10. Example: SceneKit initializer
    

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11. 3. Kind import
    1. attributes import module
    2. attributes import module.submodule
    3. attributes import importKind module.symbolName
    

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12. struct class enum protocol
    typealias func let var
    3. Kind import
    

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13. 3. Kind import
    • Individual import is only top-level
    
    • Cannot import overloaded functions separately
    

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14. Example: Conflict method name
    

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16. 1. Attributes
    
    2. Submodule import
    
    3. Kind import
    Import Options
    

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17. Can the build time be shortened?
    

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18. 4. Measuring the build times
    • made 100,000 methods
    
    • import Core vs import func Core.function0
    
    • Tried 10 times
    

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19. Basic Import Kind Import
    Average 277.645s 285.105s(+7.64s)
    Max 309.46s 312.99s(+3.53s)
    Min 273.48s 265.25s(-8.23s)
    Build time
    

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20. Basic Import Kind Import
    Filesize 7336KB 7336KB
    Md5
    0b10a59ce0a75decbb
    2f120520c4fbc1
    0b10a59ce0a75decbb
    2f120520c4fbc1
    Binary size
    

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21. Build time Binary Size Namespace
    Simple Import Same Same Optional
    Kind specify Same Same Necessary
    Pros & Cons
    

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