/// <summary>
/// Builds a <see cref="BinaryDeserializer{T}" /> for a <see cref="RecordSchema" />.
/// </summary>
/// <returns>
/// A successful <see cref="BinaryDeserializerBuilderCaseResult" /> if <paramref name="type" />
/// is not an array or primitive type and <paramref name="schema" /> is a <see cref="RecordSchema" />;
/// an unsuccessful <see cref="BinaryDeserializerBuilderCaseResult" /> otherwise.
/// </returns>
/// <inheritdoc />
public virtual BinaryDeserializerBuilderCaseResult BuildExpression(Type type, Schema schema, BinaryDeserializerBuilderContext context)
{
if (schema is RecordSchema recordSchema)
{
var underlying = Nullable.GetUnderlyingType(type) ?? type;
if (!underlying.IsArray && !underlying.IsPrimitive)
{
// since record deserialization is potentially recursive, create a top-level
// reference:
var parameter = Expression.Parameter(
Expression.GetDelegateType(context.Reader.Type.MakeByRefType(), underlying));
if (!context.References.TryGetValue((recordSchema, type), out var reference))
{
context.References.Add((recordSchema, type), reference = parameter);
}
// then build/set the delegate if it hasn’t been built yet:
if (parameter == reference)
{
Expression expression;
if (GetRecordConstructor(underlying, recordSchema) is ConstructorInfo constructor)
{
var parameters = constructor.GetParameters();
// map constructor parameters to fields:
var mapping = recordSchema.Fields
.Select(field =>
{
// there will be a match or we wouldn’t have made it this far:
var match = parameters.Single(parameter => IsMatch(field, parameter.Name));
var parameter = Expression.Parameter(match.ParameterType);
return(
Match: match,
Parameter: parameter,
Assignment: (Expression)Expression.Assign(
parameter,
DeserializerBuilder.BuildExpression(match.ParameterType, field.Type, context)));
})
.ToDictionary(r => r.Match, r => (r.Parameter, r.Assignment));
expression = Expression.Block(
mapping
.Select(d => d.Value.Parameter),
mapping
.Select(d => d.Value.Assignment)
.Concat(new[]
{
Expression.New(
constructor,
parameters
.Select(parameter => mapping.ContainsKey(parameter)
? (Expression)mapping[parameter].Parameter
: Expression.Constant(parameter.DefaultValue))),
}));
}
else
{
var members = underlying.GetMembers(MemberVisibility);
// support dynamic deserialization:
var value = Expression.Parameter(
underlying.IsAssignableFrom(typeof(ExpandoObject))
? typeof(ExpandoObject)
: underlying);
expression = Expression.Block(
new[] { value },
new[] { (Expression)Expression.Assign(value, Expression.New(value.Type)) }
.Concat(recordSchema.Fields.Select(field =>
{
var match = members.SingleOrDefault(member => IsMatch(field, member));
Expression expression;
if (match == null)
{
// always deserialize fields to advance the reader:
expression = DeserializerBuilder.BuildExpression(typeof(object), field.Type, context);
// fall back to a dynamic setter if the value supports it:
if (typeof(IDynamicMetaObjectProvider).IsAssignableFrom(value.Type))
{
var flags = CSharpBinderFlags.None;
var infos = new[] { CSharpArgumentInfo.Create(CSharpArgumentInfoFlags.None, null) };
var binder = Binder.SetMember(flags, field.Name, value.Type, infos);
expression = Expression.Dynamic(binder, typeof(void), value, expression);
}
}
else
{
Expression inner;
try
{
inner = DeserializerBuilder.BuildExpression(
match switch
{
FieldInfo fieldMatch => fieldMatch.FieldType,
PropertyInfo propertyMatch => propertyMatch.PropertyType,
MemberInfo unknown => throw new InvalidOperationException($"Record fields can only be mapped to fields and properties."),
},
field.Type,
context);
}
catch (Exception exception)
{
throw new UnsupportedTypeException(type, $"The {match.Name} member on {type} could not be mapped to the {field.Name} field on {recordSchema.FullName}.", exception);
}
expression = Expression.Assign(
Expression.PropertyOrField(value, match.Name),
inner);
}
return(expression);
}))
