Module default_typescript 

The value a TypeScript member takes when the stream does not carry it.

Table 9 of DDS-XTypes 1.3, as TypeScript. crate::default_c is the same table as C, crate::default_java as Java, crate::default_cpp as C++, and crates/wire-probe/src/default.rs is the reflective column’s; that module carries the clause quotations and the reasoning for the three kinds Table 9 does not list. Deliberately a fifth derivation and not a call into any of them: the columns are compared against each other, and a shared helper would make them agree about a mistake.

Why it is a generated function and not a literal

A literal cannot carry an aggregate. “A structure without any of the optional members and with other members set to their default values” is a newS() and one assignment per member, and writing that at every position a member can go missing would put the same answer in the generated file as many times as the type is reached — where two copies can differ. One function per type is one answer per type, which is what the C and Java columns do and for the same reason.

Why it answers with the value instead of filling one

C’s defaulter is void zd_def_T(T *v): it writes through a pointer. TypeScript has no pointer and no out-parameter, and half of Table 9’s rows are values a callee cannot mutate at all — a number, a string, an array whose length has to change. So the function returns Table 9’s value and the caller assigns it, which is the same decision one step later. It is also what makes the reader’s own shape work: every generated decoder opens with let v: T = zd_def_T();, so a position the stream does not carry is already what Table 9 says before a single octet is read.

What TypeScript forces that Java does not

Nothing is constructed at all. The materialiser emits no TypeScript class for an IDL data type — DDS-TS 1.0 §7.4 forbids one — so there is no new anywhere in this column. A union’s defaulter answers with an object literal, because the materialiser declares a union as a type over object types and a type is erased; every other aggregate has a factory function beside its interface, and it is that function the defaulter calls: crate::adapter::typescript::factory_path names it.

An absent @optional member is a missing property and not a null. §7.2.2.4.4.4.8’s “Implementations shall not provide a default value” is delete v.field here, and delete rather than v.field = undefined because the materialiser declares the field field?: T: under exactOptionalPropertyTypes — which runtime/typescript/tsconfig.json sets — assigning undefined to such a field is a tsc error, while deleting it is the operation the declaration was written for.

A fixed<P,S> is a decimal string. Table 9’s zero for it is the one spelling crates/wire-probe/src/canonical.rs accepts for that scale — "0.00" for a fixed<5,2> — and not the empty string, which is not a decimal at all.

Functions

case_label

a.b.Tag.TAG_A — the constant a union case label of an enumeration discriminator is compared against.

default_into

place = zd_def_<T>();

defaulter_from_decoder

The defaulter that goes with a decoder, by name.

defaulter_name

The defaulter function name for a type.

enumerator_constant

a.b.Enum.LITERAL — the as const object the materialiser declared, written from the file root.

explicit_default

An explicit @default as a TypeScript expression for type_.

member_default

One member’s default: its @default, or its type’s.

typescript_defaulters_called_by

The defaulters decls call, and exactly those.

typescript_defaulters_over

Build the defaulter for each of types, once per name.