Minor optimizations (#59)

[SergeiPavlov]

• Make QueryTranslationResult readonly struct

• Make QueryRequest readonly struct

• Don't load string resource until necessary

• improve is/as usages

• Optimize PrefetchHelper && make Fetcher readonluy struct

• Optimize BatchingCommandProcessor.PutTasksForExecution

• Refactor PrefetchManager.GetGraphContainer() to avoid unnecessary allocation

• Avoid double HashSet-search in TypeRegistry.Register()

• Improving refactoring of TypeDefCollection

• Use Queue.TryDequeue()

• Avoid ReadOnly-wrapping of Empty arrays. They are always immutable

• Avoid double dictionary search when removing

• Make BuildBatch() to accept IReadOnlyList arg to avoid conversions

• Make ColumnInfoRef readonly struct

• Refactor ColumnCollection

• Make TypeReference readonly struct

• Make ColumnGroup readonly struct

• Make TypeInfoRef readonly struct

[alex-kulakov]

A lot of tests failed. For example, in Xtensive.Orm.Tests.Linq namespace there are new 170 failed tests, a lot of tests from other namespaces start failing too.

[SergeiPavlov]

A lot of tests failed. For example, in Xtensive.Orm.Tests.Linq namespace there are new 170 failed tests, a lot of tests from other namespaces start failing too.

Fixed the bug

[AlexUstinov]

What if colulmnInfoRef has value but CultureInfo is null? In that case culture evaluates to null but that is probably not acceptable.

[SergeiPavlov]

I thought about this case, but it was the previous behavior, and I tried to keep it.
And it is acceptable because ComparisonRule class checks for null CultureInfo here:
https://github.com/DataObjects-NET/dataobjects-net/blob/master/Orm/Xtensive.Orm/Comparison/ComparisonRule.cs#L65

[alex-kulakov]

Tests are still failing. Take a look at the Xtensive.Orm.Tests.Storage.Prefetch.PrefetchManagerBasicTest with InvalidCastException

Unable to cast object of type System.Collections.Generic.Dictionary<System.ValueTuple<Xtensive.Orm.Key,Xtensive.Orm.Model.TypeInfo>,Xtensive.Orm.Internals.Prefetch.GraphContainer> to type <System.Collections.Generic.IEnumerable<Xtensive.Orm.Internals.Prefetch.GraphContainer>.

The Xtensive.Orm.Tests.Storage.Prefetch.PrefetchManagerAdvancedTest - the same exception (or similar, I just glanced at them, definitely InvalidCastException).

[SergeiPavlov]

Fixed InvalidCastException. All of them because dynamic casting of GraphContainersField, which implementation type changed

[alex-kulakov]

This might be a buggy line. You've changed the algorithm and nulls are not allowed to reach ComparisonRule. Some built-in comparison rules have CultureInfo set to null so null culture is valid value, I see it is taken to account all over the ComparisonRule class. ColumnInfoRef.CultureInfo can be null when ColumnInfo.CultureInfo is null which is theoretically possible but doesn't happen now, I'm not sure it should be this way but still. Did you see this?

If this causes problem it will be hard to find after few years.

[SergeiPavlov]

Yes, I thought about this semantic change.
Because ColumnInfoRef is converted to struct we cannot keep previous null-check.
But I tracked how ColumnInfo.CultureInfo may be set to null. The only way is property setter, which never called

Also we can change property type to nullable ColumnInfoRef? ColumnInfoRef.

[alex-kulakov]

The only way is property setter, which never called.

This is why I call it "hard to find". :) If somebody who doesn't know this thing or just not pays attention just set the property it will silently create a problem.

Also we can change property type to nullable ColumnInfoRef? ColumnInfoRef.
Is Checking whether ColumnInfoRef is default instance worse? Like so:

var culture = column is MappedColumn mColumn && mColumn.ColumnInfoRef != default
  ? mColumn.ColumnInfoRef.CultureInfo
  : CultureInfo.InvariantCulture;

I highly doubt that names of ColumnInfoRef that are all nulls will be valid case, right?

[SergeiPavlov]

mColumn.ColumnInfoRef != default is expensive operation. It invokes operator !=, ColumnInfoRef.Equals.

But we can check ColumnInfoRef .TypeName != null

[SergeiPavlov]

var culture = column is MappedColumn mColumn && mColumn.ColumnInfoRef != default
? mColumn.ColumnInfoRef.CultureInfo
: CultureInfo.InvariantCulture;

This was the first solution, but @AlexUstinov argued against it #207 (comment)