# Interface GuardingDynamicLinker

All Known Subinterfaces:
  `TypeBasedGuardingDynamicLinker`

All Known Implementing Classes:
  `BeansLinker, CompositeGuardingDynamicLinker, CompositeTypeBasedGuardingDynamicLinker`

public interface GuardingDynamicLinker
The base interface for language-specific dynamic linkers. Such linkers always have to produce method handles with guards, as the validity of the method handle for calls at a call site inevitably depends on some condition (at the very least, it depends on the receiver belonging to the language runtime of the linker). Language runtime implementors will normally implement the linking logic for their own language as one or more `GuardingDynamicLinker` classes. They will typically set them as `prioritized linkers` in the `DynamicLinkerFactory` they configure for themselves, and maybe also set some as `fallback linkers` to handle language-specific "property not found" etc. conditions.

Consider implementing `TypeBasedGuardingDynamicLinker` interface instead of this interface for those linkers that are based on the Java class of the objects. If you need to implement language-specific type conversions, have your `GuardingDynamicLinker` also implement the `GuardingTypeConverterFactory` interface.

Languages can export linkers to other language runtimes for `automatic discovery` using a `GuardingDynamicLinkerExporter`.

Since:
  9

- ## Method Summary

  Modifier and Type
  Method
  Description
  `GuardedInvocation`
  `getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices)`
  Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.

- ## Method Details

  - ### getGuardedInvocation

    GuardedInvocation getGuardedInvocation(LinkRequest linkRequest, LinkerServices linkerServices) throws Exception
    Creates a guarded invocation appropriate for a particular invocation with the specified arguments at a call site.
    Parameters:
      `linkRequest` - the object describing the request for linking a particular invocation
      `linkerServices` - linker services
    Returns:
      a guarded invocation with a method handle suitable for the arguments, as well as a guard condition that if fails should trigger relinking. Must return null if it can't resolve the invocation. If the returned invocation is unconditional (which is actually quite rare), the guard in the return value can be null. The invocation can also have any number of switch points for asynchronous invalidation of the linkage, as well as a `Throwable` subclass that describes an expected exception condition that also triggers relinking (often it is faster to rely on an infrequent but expected `ClassCastException` than on an always evaluated `instanceof` guard). While the linker must produce an invocation with parameter types matching those in the call site descriptor of the link request, it should not try to match the return type expected at the call site except when it can do it with only the conversions that lose neither precision nor magnitude, see `LinkerServices.asTypeLosslessReturn(MethodHandle, MethodType)` for further explanation.
    Throws:
      `Exception` - if the operation fails for whatever reason