feat: provide custom constructor setting

[lampajr]

Fixes https://github.com/jmattheis/goverter/issues/93

New feature: allow users to provide a custom constructor in order to initialize the target obj.

Usage:

        package execution

        // goverter:converter
        type Converter interface {
            // goverter:init NewOutput
            // goverter:ignore ID
            Convert(source Input) Output
        }

        type Input struct {
            ID int
            FirstName string
            LastName string
        }
        type Output struct {
            ID int
            FirstName string
            LastName string
        }
        func NewOutput() Output {
            return Output{
                ID: 0,
            }
        }

Generated converter:

        func (c *ConverterImpl) Convert(source execution.Input) execution.Output {
            var executionOutput execution.Output = execution.NewOutput()
            executionOutput.FirstName = source.FirstName
            executionOutput.LastName = source.LastName
            return executionOutput
        }

Tests:

Added some test scenarios under /scenario, all those matching constructor*.yml

[lampajr]

Hey @jmattheis,

I gave this a shot, I hope it can help :slightly_smiling_face:

Open points:

• Right now I used init as goverter setting, maybe we could use constructor or any other idea?
• The constructor can be used to set some defaults, but based on the actual generation if that field (defaulted) is not ignored.. it is going to be overridden even if nil, maybe we could thinkg about an additional setting not-override (or whatever) to skip a field assignment if nil in the source, wdyt? Obv I think this could be a followup issue if you think makes sense

[codecov[bot]]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (13d3233) 97.47% compared to head (6aa5d54) 97.87%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #96 +/- ## ========================================== + Coverage 97.47% 97.87% +0.39% ========================================== Files 38 39 +1 Lines 1663 1693 +30 ========================================== + Hits 1621 1657 +36 + Misses 29 25 -4 + Partials 13 11 -2 ``` | [Files](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis) | Coverage Δ | | |---|---|---| | [builder/default.go](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis#diff-YnVpbGRlci9kZWZhdWx0Lmdv) | `100.00% <100.00%> (ø)` | | | [builder/pointer.go](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis#diff-YnVpbGRlci9wb2ludGVyLmdv) | `100.00% <100.00%> (ø)` | | | [builder/struct.go](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis#diff-YnVpbGRlci9zdHJ1Y3QuZ28=) | `100.00% <100.00%> (ø)` | | | [config/method.go](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis#diff-Y29uZmlnL21ldGhvZC5nbw==) | `100.00% <100.00%> (ø)` | | | [generator/generator.go](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis#diff-Z2VuZXJhdG9yL2dlbmVyYXRvci5nbw==) | `100.00% <100.00%> (+3.37%)` | :arrow_up: | | [config/extend.go](https://app.codecov.io/gh/jmattheis/goverter/pull/96?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Jannis+Mattheis#diff-Y29uZmlnL2V4dGVuZC5nbw==) | `98.14% <66.66%> (ø)` | |

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[jmattheis]

@lampajr could you review the adjusted version?

[lampajr]

@lampajr could you review the adjusted version?

I just fixed a leftover in the doc (init --> default), it looks really great!!

I tried it also locally in my use case, and it worked well :muscle:

[jmattheis]

Good catch, thanks!