/Go Engineering/Phase 3

Phase 3Days 11-15

Structs, Methods, Interfaces & Generics

Go’s composition-first type system and explicit error design

Phase Goal

Design small, testable APIs using composition, narrow interfaces, errors, and restrained generics.

Progress

Notes

Open the written lectures for this course before checking off the phase topics.

Projects

Multi-Source Habitat Importer

Day 11: Structs, Composition & Invariants

Define Struct literals, field visibility, and zero-value design in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Struct literals, field visibility, and zero-value design is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Struct literals, field visibility, and zero-value design and fix it deliberately

Define Embedding versus inheritance in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Embedding versus inheritance is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Embedding versus inheritance and fix it deliberately

Define Constructors as ordinary functions in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Constructors as ordinary functions is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Constructors as ordinary functions and fix it deliberately

Define Validation boundaries and invariant ownership in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Validation boundaries and invariant ownership is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Validation boundaries and invariant ownership and fix it deliberately

Day 12: Methods & Receiver Decisions

Define Method sets and receiver syntax in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Method sets and receiver syntax is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Method sets and receiver syntax and fix it deliberately

Define Value versus pointer receiver decision rules in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Value versus pointer receiver decision rules is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Value versus pointer receiver decision rules and fix it deliberately

Define Mutation, copying, and consistency in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Mutation, copying, and consistency is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Mutation, copying, and consistency and fix it deliberately

Define Fluent APIs and why hidden mutation surprises in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Fluent APIs and why hidden mutation surprises is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Fluent APIs and why hidden mutation surprises and fix it deliberately

Day 13: Interfaces & Dependency Inversion

Define Implicit interface satisfaction in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Implicit interface satisfaction is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Implicit interface satisfaction and fix it deliberately

Define Consumer-owned narrow interfaces in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Consumer-owned narrow interfaces is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Consumer-owned narrow interfaces and fix it deliberately

Define Interface values, dynamic types, and nil-interface traps in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Interface values, dynamic types, and nil-interface traps is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Interface values, dynamic types, and nil-interface traps and fix it deliberately

Define Type assertions, type switches, and capability design in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Type assertions, type switches, and capability design is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Type assertions, type switches, and capability design and fix it deliberately

Day 14: Errors, Wrapping, Panic & Recovery

Define Errors as values and explicit control flow in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Errors as values and explicit control flow is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Errors as values and explicit control flow and fix it deliberately

Define fmt.Errorf with %w, errors.Is, and errors.As in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when fmt.Errorf with %w, errors.Is, and errors.As is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for fmt.Errorf with %w, errors.Is, and errors.As and fix it deliberately

Define Sentinel versus typed errors in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Sentinel versus typed errors is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Sentinel versus typed errors and fix it deliberately

Define When panic is justified and recovery boundaries in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when When panic is justified and recovery boundaries is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for When panic is justified and recovery boundaries and fix it deliberately

Day 15: Mini Project — Multi-Source Habitat Importer

Define Interface-driven observation-source registry in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Interface-driven observation-source registry is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Interface-driven observation-source registry and fix it deliberately

Define Typed validation and import errors in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Typed validation and import errors is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Typed validation and import errors and fix it deliberately

Define Generic collection helpers used only where justified in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Generic collection helpers used only where justified is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Generic collection helpers used only where justified and fix it deliberately

Define Project requirements, tests, and extension guide in plain language and explain the problem it solvesTrace what the Go compiler or runtime does when Project requirements, tests, and extension guide is usedWrite a tiny example, then apply it to a realistic backend taskDiagnose the beginner failure mode for Project requirements, tests, and extension guide and fix it deliberately

Capstone

Multi-Source Habitat Importer

Build a CLI that imports ranger CSV, JSON sensor dumps, and hand-entered text observations through a narrow source interface into one validated habitat record model.

Consumer-owned source interface
Wrapped errors that preserve file and row context
A new source format added without changing orchestration

Phase Complete!

After this phase, you'll be able to:

Struct literals, field visibility, and zero-value design
Embedding versus inheritance
Constructors as ordinary functions
Validation boundaries and invariant ownership
Method sets and receiver syntax
Value versus pointer receiver decision rules
Mutation, copying, and consistency
Fluent APIs and why hidden mutation surprises

You can apply Phase 3 skills in a finished, explainable Go project.

Back to all phases

Phase Goal

Day 11: Structs, Composition & Invariants

Struct literals, field visibility, and zero-value design

Embedding versus inheritance

Constructors as ordinary functions

Validation boundaries and invariant ownership

Day 12: Methods & Receiver Decisions

Method sets and receiver syntax

Value versus pointer receiver decision rules

Mutation, copying, and consistency

Fluent APIs and why hidden mutation surprises

Day 13: Interfaces & Dependency Inversion

Implicit interface satisfaction

Consumer-owned narrow interfaces

Interface values, dynamic types, and nil-interface traps

Type assertions, type switches, and capability design

Day 14: Errors, Wrapping, Panic & Recovery

Errors as values and explicit control flow

fmt.Errorf with %w, errors.Is, and errors.As

Sentinel versus typed errors

When panic is justified and recovery boundaries

Day 15: Mini Project — Multi-Source Habitat Importer

Interface-driven observation-source registry

Typed validation and import errors

Generic collection helpers used only where justified

Project requirements, constraints & review

Multi-Source Habitat Importer

Phase Complete!