Constructor, explicit, and collection DI

_{Beginner → Intermediate. Annotations, explicit targets, collections.}

Annotate a constructor parameter. Melder builds the graph.

class ReportService:
    def __init__(self, database: Database) -> None:   # ← injected
        self.database = database

book.bind(spell=Database, existence="unique")
book.bind(spell=ReportService, existence="unique")
conduit = book.conjure()

report = conduit.meld("ReportService")

When an annotation isn't specific enough — two implementations of one shape, or a named binding — declare the target with SpellMap as the parameter default:

class Consumer:
    def __init__(self, store=md.SpellMap(PrimaryStore)) -> None:
        self.store = store

SpellMap takes the full address: a concrete spell, a spellframe, a binding_name, or a combination. It obeys an exactly-one law — a target that matches zero spells or several fails at conjure(), not at runtime.

Ask for a list and get every implementation — the plugin pattern in one annotation:

class Dispatcher:
    def __init__(self, handlers: list[Handler]) -> None:   # ← all of them
        self.handlers = handlers

book.bind(spell=EmailHandler, existence="unique",
          spellframe=Handler, binding_name="email")
book.bind(spell=SmsHandler, existence="unique",
          spellframe=Handler, binding_name="sms")

Runnable examples

Constructor di by annotation — Intermediate 15
Spellmap defaults — Intermediate 16
Collection di — Intermediate 17

All intermediate examples · Level contents · Full contents

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