lang-haxe

Haxe — Verified Gotchas

String Interpolation: Single Quotes Only

Inverted from most languages. Double quotes are plain strings.

var name = "world";
var greeting = 'Hello, $name!';        // ✓ Simple variable — no braces
var result = 'Sum is ${a + b}';        // ✓ Expression — braces required
var plain = "No $interpolation here";  // ✗ Literal text, no parsing

• $name for simple variables — NO braces
• ${expr} only for expressions (field access, math, function calls)
• '${_name}' is wrong → '$_name'

Escaping a literal $: use $$, NEVER \$

To put a literal $ in a single-quoted string, double it: $$. \$ is not a valid escape sequence — haxe rejects it with Invalid escape sequence \$ (the recognized escapes are \t \n \r \" \' \\ \xXX \uXXXX; \$ is not among them).

var a = 'price is $$5';          // ✓ → "price is $5"
var b = 'unterminated $${ here'; // ✓ → "unterminated ${ here"  (escape the $, the { is literal)
var c = 'cost \$5';              // ✗ COMPILE ERROR: Invalid escape sequence \$
var d = "cost $5";               // ✓ double quotes never interpolate → literal "cost $5"

So for a literal $ (or a literal ${) the two correct forms are $$ inside '...' or just use "..." (no interpolation at all). Reach for double quotes when the string is mostly literal $/${; use $$ when you also want interpolation elsewhere in the same string.

Compile-traps — index (details: references/compile-traps.md)

A Haxe compile error whose message does not obviously name the cause → Read references/compile-traps.md BEFORE trying fixes. It covers: String has no field replace (using StringTools) · Cannot access property in a subclass ((default,null)) · Default argument value should be constant (enum ctor with args) · @:privateAccess placement · typedef→enum field-access breakage · Type not found for return types / sub-module types (imports) · Unknown identifier in single-quoted test fixtures with $ (MISLEADING — points at the call argument; use double quotes, scan EVERY touched test file) · block comments dying on inner */ · Cannot create closure on inline closure · Expected ) on for (x:Type in xs) · Unexpected @ on enum-ctor param metadata · keyword collisions (untyped, cast, dynamic, …) · regex ^A|B parsing as (^A)|B — SILENT mid-buffer matches, wrap ^(?:A|B) and treat matchedPos().pos != 0 as no-match.