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+# Construction and Private Memory
+
+English | [日本語](README.ja.md)
+
+[Previous: SSA Before Types Are Known](../chapter-incomplete-types/README.md) |
+
+
+The previous chapter built SSA before it knew all the types.  This chapter uses
+that freedom to move object initialization into functions.  The new problem is
+memory: a constructor must remember what it has written to this object without
+mixing those values with every older object of the same type.
+
+We keep the object private while it is built, then publish its initialized
+fields to public memory.  No partially-built instance can ever escape (unlike
+some languages where the `this` object can escape before final fields are
+actually set and final).  Finding all the ways an object can escape comes next.
+
+
+## Constructors are calls
+
+```simple
+struct Box {
+    int x = 7;
+    int[] data;
+    new Box = { int n ->
+        data = new int[2];
+        x = n;
+        data[0] = x + 1;
+    };
+    val get = { -> x + data[0]; };
+};
+val a = new Box(arg);
+val b = new Box(arg + 10);
+return a.get() * 100 + b.get();
+```
+
+For `arg == 2`, this returns `525`.  Each call allocates its own `Box` and array.
+The declaration `new Box = { ... };` supplies the constructor body.  The body
+still parses as an anonymous function; `new` marks its role as a constructor.
+The expression `new Box(...)` allocates an object and calls it.  A constructor
+returns *private memory*, not a source-level value.
+
+The parser creates two helpers for each struct:
+
+* `Box.<init>` runs the field initializers, in declaration order.
+* `Box.<new>` allocates the object, calls `<init>`, calls the user constructor
+  if there is one, publishes the fields, and returns the pointer.
+
+The initializer and user constructor receive hidden `self` and `#selfMem`
+arguments.  *Public* memory still travels through input 1 of calls and returns;
+the *private* memory is a separate argument and result.  A constructor can allocate
+a public array or update an already public object without losing its own field state.
+
+The old `new Box { ... }` syntax remains an inline construction block. It runs
+the field initializers, then its block, then publishes; it does not also call
+the named user constructor.  Ordinary methods still use public memory.
+
+
+## Fields are local values during construction
+
+Public memory describes all objects with a given field alias. A public Store
+therefore combines the new value with values already in that alias.
+E.g. writing `a.x = 3` cannot prove that `b.x` is also 3, so the general `.x`
+field alias is usually some form of `BOTTOM`.
+
+During construction we already know which object each field belongs to, and
+the language prevents its partial state from becoming visible.  The parser can
+therefore keep its fields as local SSA values.  Both `x` and `self.x` refer to
+the same local slot, although an argument named `x` can shadow the bare name.
+An assignment updates that slot; it does not emit a Store.
+
+Branches merge the values with ordinary Phis.  Loops use ordinary loop Phis,
+including their existing integer range widening. For example:
+
+```simple
+struct Counter {
+    int x;
+    new Counter = { int n -> while (x < n) x++; };
+};
+return new Counter(arg).x;
+```
+
+The constructor loop carries the value of `x`. It needs no memory Phi and
+performs no field Store on each trip.  At the constructor exit, the compiler
+stores the final value into the new object.  This is the result scalar
+replacement would give us, built directly from the construction rules.
+
+Private memory is still useful at the helper boundaries. `NewNode` produces
+the pointer and its initial private memory. The hidden initializer computes
+defaults as local values and emits ordinary initializing Stores at exit.  The
+user constructor loads those fields into local slots, computes their final
+values, and emits its own exit Stores.  Each Store produces one precise alias;
+`MemMergeNode` packages the slices for the helper result. `TypeMem` records the
+field values across the call, without joining them with older objects.
+
+```text
+New -> <init>: local defaults -> field Stores
+    -> constructor: local values and Phis -> field Stores
+    -> publication -> public field aliases
+```
+
+Constructor signatures are bound at their declarations.  Their bodies are
+parsed after the struct's field list closes, so even a later-declared field
+has a local slot before a branch or loop is built.
+
+Arrays use the same publication boundary: zero-filled elements and an
+initialized length are published before the array is returned.  Required
+non-null fields have no legal zero default.  Reading one before it is written
+is an error.
+
+
+## Publish only after completion
+
+`EscapeNode` publishes one field.  It consumes control, public memory, private
+memory, and `self`; its result joins the field's value into the public alias.
+Publication has no machine instruction, but its memory edges keep initializing
+Stores before later Loads and Stores.  Every field is published independently, 
+and scheduling may well interleave the initializing writes from many unrelated
+allocations and public memory updates.
+
+Before publication, every required field must be initialized on every live
+path.  This is rejected when `arg` can be zero:
+
+```simple
+struct Box {
+    int[] data;
+    new Box = { int n -> if (n) data = new int[2]; };
+};
+return new Box(arg);
+```
+
+This is rejected because `int[] data` requires a non-null initial value, and if
+`arg` is null, `data` is never set not-null.  This check is based on the type
+of every field at the constructor exit; if type analysis (e.g. SCCP) determines
+the field is set, the code is good; if not then not.
+
+## Build and check
+
+From this directory:
+
+```bash
+make lib tests CTAGS=
+```
+
+Or from the repository root:
+
+```bash
+make tests CHAPTERS=chapter-construction CTAGS=
+```
+
+`ConstructionTest` exercises constructor calls, independent instances, dynamic
+defaults, completion errors, forward fields and methods, private loops, native
+execution, and ARM/RISC-V execution. The inherited language, memory, lattice,
+and backend suites run alongside it.