Add method for messagepack messages to assert type #45
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This is a simple method for letting messages assert that they are one of a known set of types and raise a nicely formatted error if the assertion fails. Unfortunately, this cannot be expressed in the type system in a clean way at present. A TypeGuard cannot be defined as a union over a sequence-type argument to a method. We don't want to build fragile code which is based on stringized annotations being ealuated at runtime, so for now this just focuses on giving us the runtime safety which we'll care about in our applications. Additional `assert` calls, `cast` calls, or `type:ignore` comments can still be used to narrow types under type checking.
chris-janidlo
requested changes
Jun 13, 2022
chris-janidlo
approved these changes
Jun 13, 2022
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This is a simple method for letting messages assert that they are one
of a known set of types and raise a nicely formatted error if the
assertion fails.
Unfortunately, this cannot be expressed in the type system in a clean
way at present. A TypeGuard cannot be defined as a union over a
sequence-type argument to a method.
We don't want to build fragile code which is based on stringized
annotations being ealuated at runtime, so for now this just focuses on
giving us the runtime safety which we'll care about in our
applications. Additional
assertcalls,castcalls, ortype:ignorecomments can still be used to narrow types under typechecking.