What Code Generation Can Do for You

Marc-Antoine Sauvé Hopper

Hopper Creates Trust from DataWe process 300 billion flight prices each month to build trust and optimize customer interactions.

Repetitive tasks are

Boring Error prone Counterproductive

Sourcery

Code generation No reflection Flexible

What is it?Standalone application

What is it?Standalone application

Scan the source code

What is it?Standalone application

Scan the source code

Uses templates

What is it?Standalone application

Scan the source code

Uses templates

Generate source code

What is it?Standalone application

Scan the source code

Uses templates

Generate source code

Can read code and comments

public class Foo {}

Foo.swift

{% for type in types.all %}extension {{ type.name }} {{% if type.accessLevel == "public" %}

public var name: String {return "{{ type.name }}"

}{% endif %}}{% endfor %}

AutoClassName.stencil

public class Foo {}

Foo.swift

{% for type in types.all %}extension {{ type.name }} {{% if type.accessLevel == "public" %}

public var name: String {return "{{ type.name }}"

}{% endif %}}{% endfor %}

AutoClassName.stencil

public class Foo {}

Foo.swift

{% for type in types.all %}extension {{ type.name }} {{% if type.accessLevel == "public" %}

public var name: String {return "{{ type.name }}"

}{% endif %}}{% endfor %}

AutoClassName.stencil

public class Foo {}

Foo.swift

{% for type in types.all %}extension {{ type.name }} {{% if type.accessLevel == "public" %}

public var name: String {return "{{ type.name }}"

}{% endif %}}{% endfor %}

AutoClassName.stencil

public class Foo {}

Foo.swift

{% for type in types.all %}extension {{ type.name }} {{% if type.accessLevel == "public" %}

public var name: String {return "{{ type.name }}"

}{% endif %}}{% endfor %}

AutoClassName.stencil

public class Foo {}

extension Foo {public var name: String {

return "Foo"}

}

Foo.swift

AutoClassName.generated.swift

Sourcery

Before build Watch files Manual

Real Swift problemListing enum

public enum SuperPower { case HeatVision case SuperSpeed case SuperStrength case XrayVision case SuperIntelligence}

models.swift

protocol AutoCases { }public enum SuperPower: AutoCases { case HeatVision case SuperSpeed case SuperStrength case XrayVision case SuperIntelligence}

models.swift

{% for enum in types.implementing.AutoCases|enum %}{{ enum.accessLevel }} extension {{ enum.name }} { static public let count: Int = {{ enum.cases.count }} {% if not enum.hasAssociatedValues %} static public let allCases: [{{ enum.name }}] = [ {% for case in enum.cases %} .{{ case.name }}{% if not forloop.last %},{% endif %} {% endfor %}] {% endif %}}{% endfor %}

AutoCases.stencil

{% for enum in types.implementing.AutoCases|enum %}{{ enum.accessLevel }} extension {{ enum.name }} { static public let count: Int = {{ enum.cases.count }} {% if not enum.hasAssociatedValues %} static public let allCases: [{{ enum.name }}] = [ {% for case in enum.cases %} .{{ case.name }}{% if not forloop.last %},{% endif %} {% endfor %}] {% endif %}}{% endfor %}

AutoCases.stencil

{% for enum in types.implementing.AutoCases|enum %}{{ enum.accessLevel }} extension {{ enum.name }} { static public let count: Int = {{ enum.cases.count }} {% if not enum.hasAssociatedValues %} static public let allCases: [{{ enum.name }}] = [ {% for case in enum.cases %} .{{ case.name }}{% if not forloop.last %},{% endif %} {% endfor %}] {% endif %}}{% endfor %}

AutoCases.stencil

public extension SuperPower { static let count: Int = 5 static public let allCases: [SuperPower] = [ .HeatVision, .SuperSpeed, .SuperStrength, .XrayVision, .SuperIntelligence ]}

AutoCases.generated.swift

Sourcery

Readable code Debuggable DRY

Equatable

// swiftlint:disable file_length// [...] Removed some boilerplate to enhance readability{% macro compareVariables variables %} {% for variable in variables where variable.readAccess != "private" and variable.readAccess != "fileprivate" %}{% if not variable.annotations.skipEquality %}guard {% if not variable.isOptional %}{% if not variable.annotations.arrayEquality %}lhs.{{ variable.name }} == rhs.{{ variable.name }}{% else %}compareArrays(lhs: lhs.{{ variable.name }}, rhs: rhs.{{ variable.name }}, compare: ==){% endif %}{% else %}compareOptionals(lhs: lhs.{{ variable.name }}, rhs: rhs.{{ variable.name }}, compare: ==){% endif %} else { return false }{% endif %} {% endfor %}{% endmacro %}

// MARK: - AutoEquatable for classes, protocols, structs{% for type in types.implementing.AutoEquatable|!enum %}

// MARK: - {{ type.name }} AutoEquatable{% if not type.kind == "protocol" and not type.based.NSObject %}extension {{ type.name }}: Equatable {}{% endif %}{% if type.supertype.based.Equatable or type.supertype.implements.AutoEquatable %}THIS WONT COMPILE, WE DONT SUPPORT INHERITANCE for AutoEquatable{% endif %}{{ type.accessLevel }} func == (lhs: {{ type.name }}, rhs: {{ type.name }}) -> Bool { {% if not type.kind == "protocol" %} {% call compareVariables type.storedVariables %} {% else %} {% call compareVariables type.allVariables %} {% endif %} return true}{% endfor %}

// Keeps going for a while adding some code for enums

AutoEquatable.stencil

// MARK: - SuperHero AutoEquatableextension SuperHero: Equatable {}public func == (lhs: SuperHero, rhs: SuperHero) -> Bool { guard lhs.name == rhs.name else { return false } guard lhs.superPowers == rhs.superPowers else { return false } return true}

AutoEquatable.generated.swift

// MARK: - SuperPower AutoEquatableextension SuperPower: Equatable {}public func == (lhs: SuperPower, rhs: SuperPower) -> Bool { switch (lhs, rhs) { case (.HeatVision, .HeatVision): return true case (.SuperSpeed(let lhs), .SuperSpeed(let rhs)): if lhs.speed != rhs.speed { return false } if lhs.duration != rhs.duration { return false } return true // [ Skipped some code for readability ] default: return false }}

AutoEquatable.generated.swift

public class SuperHero: AutoEquatable { public let name: String // sourcery: skipEquality public let sidekick: SuperHero? public let superPowers: [SuperPower]}

Annotations

Sourcery

Test once Avoid human mistakes Low maintenance cost

ClosureType

DictionaryType

ArrayType TupleElement

TupleType

TypeName

Subscript

MethodParameter

Method

Variable

AssociatedValue

Enum

EnumCase

ClassTypes

Protocol

Struct

GenericType

GenericTypeParameter

Attribute

What’s bad?Hard to read the template

Hard to read the template

Hard to write the template

What’s bad?

Hard to read the template

Hard to write the template

Poor support in the IDEs

What’s bad?

Hard to read the template

Hard to write the template

Poor support in the IDEs

Can be slow to compile

What’s bad?

Hard to read the template

Hard to write the template

Poor support in the IDEs

Can be slow to compile

Annotations are not type checked

What’s bad?

AppCode

Visual Studio Code

Still worth it!Saves a lot of time!

Questions?

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