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7y ago 46:54

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Managing Dependencies

iteration

To collaborate, an object must know something about others. Knowing creates a dependency. If not managed carefully, these dependencies will strangle your application

Recognizing Dependencies

An object has a dependency when it knows:

The name of another class.
- Gear expects a class named Wheel to exist
The name of a message that it intends to send to someone other than self.
- Gear expects a Wheel instance to respond to diameter
The arguments that a message requires.
- Gear knows that Wheel.new requires a rim and a tire
The order of those arguments.
- Gear knows the first argument to Wheel.new should be rim and the second should be tire

Writing Loosely Coupled Code

Inject Dependencies

see 1_inject_dependencies.rb

Referring to a class by its name inside of another class is bad.
If the name of Wheel class changes, the gear_inches method must also change
The bigger problem is that gear_inches is explicitly saying that it is only willing to calculate gear inches for instances of Wheel
Gear will only collaborate with any other kind of object even if that object has a diameter and uses gears!

It's is not the class of the object that's important, it's the message you plan to send to it.

Gear needs access to an object that can respond to diameter - a duck type
We can use a technique called dependency injection to move the creation of a new Wheel instance outside of the class

Isolate Dependencies

see 2_isolate_dependencies.rb

Isolate Instance Creation

Sometimes you can't break all unnecessary dependencies, but you can isolate them
The first technique moves Wheel.new from gear_inches and into Gear's initialize method
The next alternative isolates the creation of a Wheel into its own wheel method

Isolate Vulnerable External Messages

gear_inches depends on Gear responding to wheel and wheel responding to diameter
by creating a different diameter method to hold wheel.diameter, we remove the dependency within gear_inches

Remove Argument-Order Dependencies

see 3_remove_arg_orer_dependencies.rb

Use Hashes for Initialization Arguments

arguments of our initialize method must be passed in the correct order. we can pass an object instead to remove this dependency

Explicitly Define Defaults

we can use the fetch method to set defaults when using hashes in our initialize method
fetch expects the key you're fetching to be in the hash and supplies several options for handling missing keys
fetch will only set the default if the key is not found in the hash

Managing Dependency Direction

All examples thus far have shown Gear depending on Wheel or diameter - but the code could have easily been written so that Wheel depends on Gear or ratio

Choosing Dependency Direction

Depend on things that change less often

John’s pick - Pick Krisp -https://krisp.ai

78 episodes

#Business #Design #Ruby On Rails #Ruby #Code #JP Sio - Web Developers #John Jacob #Web Development #Tech #Software Development #Iteration #Programming #JavaScript

Managing Dependencies

iteration

96 subscribers

published 7y ago

MP3•Episode home

Chapter 3: Managing Dependencies

To collaborate, an object must know something about others. Knowing creates a dependency. If not managed carefully, these dependencies will strangle your application

Recognizing Dependencies

An object has a dependency when it knows:

The name of another class.
- Gear expects a class named Wheel to exist
The name of a message that it intends to send to someone other than self.
- Gear expects a Wheel instance to respond to diameter
The arguments that a message requires.
- Gear knows that Wheel.new requires a rim and a tire
The order of those arguments.
- Gear knows the first argument to Wheel.new should be rim and the second should be tire

Writing Loosely Coupled Code

Inject Dependencies

see 1_inject_dependencies.rb

Referring to a class by its name inside of another class is bad.
If the name of Wheel class changes, the gear_inches method must also change
The bigger problem is that gear_inches is explicitly saying that it is only willing to calculate gear inches for instances of Wheel
Gear will only collaborate with any other kind of object even if that object has a diameter and uses gears!

It's is not the class of the object that's important, it's the message you plan to send to it.

Gear needs access to an object that can respond to diameter - a duck type
We can use a technique called dependency injection to move the creation of a new Wheel instance outside of the class

Isolate Dependencies

see 2_isolate_dependencies.rb

Isolate Instance Creation

Sometimes you can't break all unnecessary dependencies, but you can isolate them
The first technique moves Wheel.new from gear_inches and into Gear's initialize method
The next alternative isolates the creation of a Wheel into its own wheel method

Isolate Vulnerable External Messages

gear_inches depends on Gear responding to wheel and wheel responding to diameter
by creating a different diameter method to hold wheel.diameter, we remove the dependency within gear_inches

Remove Argument-Order Dependencies

see 3_remove_arg_orer_dependencies.rb

Use Hashes for Initialization Arguments

arguments of our initialize method must be passed in the correct order. we can pass an object instead to remove this dependency

Explicitly Define Defaults

we can use the fetch method to set defaults when using hashes in our initialize method
fetch expects the key you're fetching to be in the hash and supplies several options for handling missing keys
fetch will only set the default if the key is not found in the hash

Managing Dependency Direction

All examples thus far have shown Gear depending on Wheel or diameter - but the code could have easily been written so that Wheel depends on Gear or ratio

Choosing Dependency Direction

Depend on things that change less often

John’s pick - Pick Krisp -https://krisp.ai

78 episodes

#Business #Design #Ruby On Rails #Ruby #Code #JP Sio - Web Developers #John Jacob #Web Development #Tech #Software Development #Iteration #Programming #JavaScript

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iteration « » Managing Dependencies

Chapter 3: Managing Dependencies

Recognizing Dependencies

Writing Loosely Coupled Code

Inject Dependencies

Isolate Dependencies

Remove Argument-Order Dependencies

Managing Dependency Direction

Choosing Dependency Direction

Managing Dependencies

Chapter 3: Managing Dependencies

Recognizing Dependencies

Writing Loosely Coupled Code

Inject Dependencies

Isolate Dependencies

Remove Argument-Order Dependencies

Managing Dependency Direction

Choosing Dependency Direction

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Managing Dependencies