C# source profile and native APIs

Without surfaces: ["js"], the C# target uses its native source profile.

C# primitive aliases

import type {
  bool,
  byte,
  int,
  long,
  double,
} from "@tsonic/csharp/types.js";

export function widen(value: int): long {
  return value as long;
}

The aliases use familiar C# names while retaining exact source primitive facts. Neutral libraries may instead use int32, int64, and float64 from @tsonic/core/types.js.

C# marker aliases

import { Int32 } from "@tsonic/dotnet/System.js";
import { defaultof, out } from "@tsonic/csharp/lang.js";
import type { int } from "@tsonic/csharp/types.js";

export function parse(): int {
  let output = defaultof<int>();
  return Int32.TryParse("42", out(output)) ? output : defaultof<int>();
}

out, ref, inref, and defaultof are C# spellings for neutral semantic contracts. The selected provider signature proves that the second argument of TryParse is write-only; the target does not infer that from the out spelling alone. ptr and fnptr request native C# pointer and function-pointer types; they are not aliases for the safe neutral Pointer<T> location.

.NET virtual imports

A namespace maps to a virtual module:

import { DateTime, TimeSpan } from "@tsonic/dotnet/System.js";
import { Dictionary } from "@tsonic/dotnet/System.Collections.Generic.js";

The built-in provider resolves framework references and configured assemblies, loads only the requested declaration closure, and preserves exact type family, arity, member, signature, by-reference, generic constraint, nullability, and attribute information. A missing or unsupported native declaration fails at the import/provider boundary.

JavaScript surface

Select the JS source profile explicitly:

{
  "targets": [{ "id": "csharp", "surfaces": ["js"] }]
}

const values = [1, 2, 3];
console.log(values.map((value) => value * 2).join(","));

This changes the active ambient source profile and adds the C# JS runtime. It does not disable explicit @tsonic/dotnet/* provider imports.

See the exact source-module reference and .NET provider reference.