private static Func <TIn, TOut> CompileFromFingerprint(Expression <Func <TIn, TOut> > expr)
{
ExpressionFingerprintChain fingerprint = FingerprintingExpressionVisitor.GetFingerprintChain(expr, out List <object> capturedConstants);
if (fingerprint != null)
{
var del = _fingerprintedCache.GetOrAdd(fingerprint, _ =>
{
// Fingerprinting succeeded, but there was a cache miss. Rewrite the expression
// and add the rewritten expression to the cache.
var hoistedExpr = HoistingExpressionVisitor <TIn, TOut> .Hoist(expr);
return(hoistedExpr.Compile());
});
return(model => del(model, capturedConstants));
}
// couldn't be fingerprinted
return(null);
}
public void Hoist()
{
// Arrange
Expression <Func <string, int> > expr = s => (2 * s.Length) + 1;
// Act
Expression <Hoisted <string, int> > hoisted = HoistingExpressionVisitor <string, int> .Hoist(
expr
);
// Assert
// new expression should be (s, capturedConstants) => (int)(capturedConstants[0]) * s.Length + (int)(capturedConstants[1])
// with fingerprint [ LAMBDA:Hoisted<string, int>, OP_ADD:int, OP_MULTIPLY:int, OP_CAST:int, INDEX(List<object>.get_Item):object, PARAM(0):List<object>, CONST:int, MEMBER(String.Length):int, PARAM(1):string, OP_CAST:int, INDEX(List<object>.get_Item):object, PARAM(0):List<object>, CONST:int, PARAM(1):string, PARAM(0):List<object> ]
List <object> capturedConstants;
ExpressionFingerprintChain fingerprint =
FingerprintingExpressionVisitor.GetFingerprintChain(hoisted, out capturedConstants);
Assert.Equal(new object[] { 0, 1 }, capturedConstants.ToArray()); // these are constants from the hoisted expression (array indexes), not the original expression
FingerprintingExpressionVisitorTest.AssertChainEquals(
fingerprint,
new LambdaExpressionFingerprint(
ExpressionType.Lambda,
typeof(Hoisted <string, int>)
),
new BinaryExpressionFingerprint(
ExpressionType.Add,
typeof(int),
null /* method */
),
new BinaryExpressionFingerprint(
ExpressionType.Multiply,
typeof(int),
null /* method */
),
new UnaryExpressionFingerprint(
ExpressionType.Convert,
typeof(int),
null /* method */
),
new IndexExpressionFingerprint(
ExpressionType.Index,
typeof(object),
typeof(List <object>).GetProperty("Item")
),
new ParameterExpressionFingerprint(
ExpressionType.Parameter,
typeof(List <object>),
0 /* parameterIndex */
),
new ConstantExpressionFingerprint(ExpressionType.Constant, typeof(int)),
new MemberExpressionFingerprint(
ExpressionType.MemberAccess,
typeof(int),
typeof(string).GetProperty("Length")
),
new ParameterExpressionFingerprint(
ExpressionType.Parameter,
typeof(string),
1 /* parameterIndex */
),
new UnaryExpressionFingerprint(
ExpressionType.Convert,
typeof(int),
null /* method */
),
new IndexExpressionFingerprint(
ExpressionType.Index,
typeof(object),
typeof(List <object>).GetProperty("Item")
),
new ParameterExpressionFingerprint(
ExpressionType.Parameter,
typeof(List <object>),
0 /* parameterIndex */
),
new ConstantExpressionFingerprint(ExpressionType.Constant, typeof(int)),
new ParameterExpressionFingerprint(
ExpressionType.Parameter,
typeof(string),
1 /* parameterIndex */
),
new ParameterExpressionFingerprint(
ExpressionType.Parameter,
typeof(List <object>),
0 /* parameterIndex */
)
);
}
