Darius Rueckert 572ec4a5a5 Rework Expression creation and insertion ...

Objects of 'Expression' can now be freely created and copied around.
This creation does NOT add them to the active ExpressionGraph any
more. The insertion into the graph is now done by ExpressionRef,
which explicitly call graph.add(...) in each operation.

This change brings the following advantages:

1. 'Expression' is now stand-alone and side-effect free
   - Remove the dependency Expression->ExpressionGraph
   - Expressions can be created by the optimizer

2. Explicit graph insertion
  - Previously CreateCompileTimeConstant not only created an
    expression, but also inserted it into the active graph. Now
    this insertion is done explicitly by ExpressionRef

3. It is now easier to insert new types and members
  - Should be straight forward now, because we got rid of the
    3-way dependency
  - This is a preparation patch for the new return-type member in
    https://ceres-solver-review.googlesource.com/c/ceres-solver/+/16224

Change-Id: Icef2fe529a4db001a10d1fb6816c9dc681b14ff2

2019-12-06 13:35:21 +01:00

..

ceres

Rework Expression creation and insertion

2019-12-06 13:35:21 +01:00