/// <summary>
/// Contructs immutable object from existing one with changed property specified by lambda expression.
/// </summary>
/// <typeparam name="TInstance">Immutable object type.</typeparam>
/// <typeparam name="TValue">Value to set type.</typeparam>
/// <param name="source">Original immutable object.</param>
/// <param name="expression">Navigation property specifying what to change.</param>
/// <param name="value">Value to set in the resulting object.</param>
/// <returns>Immutable object with changed property.</returns>
public TInstance With <TInstance, TValue>(TInstance source, Expression <Func <TInstance, TValue> > expression, TValue value)
{
if (source == null)
{
throw new ArgumentNullException(nameof(source));
}
if (expression == null)
{
throw new ArgumentNullException(nameof(expression));
}
var processContext = new ProcessContext <TInstance>()
{
Source = source,
Target = value as object,
SourceParameterExpression = expression.Parameters.Single(),
InstanceExpression = expression.Body
};
var actualValue = (TValue)ResolveInstance(processContext);
if (object.Equals(actualValue, value))
{
return(source);
}
while (processContext.InstanceExpression != processContext.SourceParameterExpression)
{
if (TryProcessMemberExpression(processContext))
{
continue;
}
throw new NotSupportedException($"Unable to process expression. Expression: '{processContext.InstanceExpression}'.");
}
var target = (TInstance)processContext.Target;
processContext.AffectedProperties.Reverse();
OnEmit?.Invoke(source, target, value, processContext.AffectedProperties.ToArray());
return(target);
}
private object ResolveInstance <TSource>(ProcessContext <TSource> processContext)
{
var key = new InstanceExpressionCacheKey(typeof(TSource), processContext.InstanceExpression);
var compiledExpression = default(ResolveInstanceDelegate <TSource>);
if (ResolveInstanceExpressionCache.TryGetValue(key, out var resolveInstanceDelegate))
{
compiledExpression = (ResolveInstanceDelegate <TSource>)resolveInstanceDelegate;
}
else
{
var instanceConvertExpression = Expression.Convert(processContext.InstanceExpression, typeof(object));
var lambdaExpression = Expression.Lambda <ResolveInstanceDelegate <TSource> >(instanceConvertExpression, processContext.SourceParameterExpression);
compiledExpression = lambdaExpression.Compile();
ResolveInstanceExpressionCache[key] = compiledExpression;
}
return(compiledExpression.Invoke(processContext.Source));
}
private bool TryProcessMemberExpression <TSource>(ProcessContext <TSource> processContext)
{
if (processContext.InstanceExpression is MemberExpression memberExpression && memberExpression.Member is PropertyInfo property)
{
processContext.InstanceExpression = memberExpression.Expression;
var result = processContext.Target;
var type = memberExpression.Expression.Type;
var instance = ResolveInstance(processContext);
var activationContext = GetActivationContext(type, type);
var arguments = ResolveActivatorArguments(activationContext.ParameterResolvers, property, instance, ref result);
processContext.Target = activationContext.Activator.Invoke(arguments);
processContext.AffectedProperties.Add(property.Name);
return(true);
}
return(false);
}
