Lesson 29 of 55
10 mins readPython Inner & Outer Constructors
In Plain English
Constructors instantiate structs. Inner constructors have access to the special new() function to enforce invariants; outer constructors provide convenient alternative signatures.
Deep Dive: How It Works
Default Constructor: Automatically generated if no inner constructor is defined.
Inner Constructor: Defined inside the struct body. Replaces the default constructor to validate arguments before calling new(args...).
Outer Constructor: Defined outside the struct to provide convenience overloads (e.g. constructing from a single argument).
Core Rules to Remember
Invariant Enforcement with new(): Prevent invalid objects from being constructed at runtime.
Outer Convenience Methods: Provide default parameters or format conversions seamlessly.
Live Interactive Example
Hit Run Code to see it liveOrdered Interval with Inner Constructor
Python 3.12
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Output Console
Click "Run Code" to view the rendered output.
How it works: new() initializes the struct fields safely after the validation check passes.
Your Turn: Micro Challenge
No pressure! Edit the starter code below and test your solution with instant feedback.
Micro Exercise
Validate Positive Radius
- Define `struct Circle radius::Float64` with an inner constructor checking `r > 0`.
- Create `c = Circle(3.5)` and print `"Radius: $(c.radius)"`.
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Sandbox Output
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