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LibJS: Support array holes, encoded as empty JS::Value

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This patch adds a new kind of JS::Value, the empty value.
It's what you get when you do JSValue() (or most commonly, {} in C++.)

An empty Value signifies the absence of a value, and should never be
visible to JavaScript itself. As of right now, it's used for array
holes and as a return value when an exception has been thrown and we
just want to unwind.

This patch is a bit of a mess as I had to fix a whole bunch of code
that was relying on JSValue() being undefined, etc.
This commit is contained in:
Andreas Kling 2020-04-06 20:24:45 +02:00
parent 5495f06af5
commit bdffc9e7fb
9 changed files with 102 additions and 35 deletions
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7
Libraries/LibJS/Runtime/Value.h
View file

@ -36,6 +36,7 @@ namespace JS {
class Value {
public:
enum class Type {
Empty,
Undefined,
Null,
Number,
@ -44,6 +45,7 @@ public:
Boolean,
};
bool is_empty() const { return m_type == Type::Empty; }
bool is_undefined() const { return m_type == Type::Undefined; }
bool is_null() const { return m_type == Type::Null; }
bool is_number() const { return m_type == Type::Number; }
@ -56,10 +58,7 @@ public:
bool is_nan() const { return is_number() && __builtin_isnan(as_double()); }
bool is_infinity() const { return is_number() && __builtin_isinf(as_double()); }
Value()
: m_type(Type::Undefined)
{
}
Value();
explicit Value(bool value)
: m_type(Type::Boolean)